Speaking to Aljazeera.net, al-Barghouti's legal representative, Khadir Shkirat said the 44-year old leader of the PLO's Fatah Movement in the West Bank was suffering from back, throat and stomach problems as a result of the conditions in which he is being kept.
Al-Barghouti's popularity among Palestinians is second only to that of Palestinian president Yasir Arafat.
Since his detention in April 2002, the lawyer said, al-Barghouti has been kept in isolation in "a dirty prison cell measuring 2m by 1.5m".
Shkirat says he has asked on many occasions for a doctor to attend to his client, who had been suffering from a slipped disc before his detention.
"But he has never ever had a medical doctor attend to him. He has asked many times."
All the Israelis have done, says his lawyer, is to send a nurse with medicine to ease his pain.
The cramped and humid prison cell conditions, as well as torture and interrogation have added to his health problems.
"When I visited him on Tuesday afternoon, he was not even able to sit up and speak to me", stressed Shkirat, a few hours after seeing his client.
Al-Barghouti, who is an elected member of the Palestinian Legislative Council, is facing trial on charges of murdering or abetting the killings of 26 people in the present intifada. He also faces charges of membership and activity in a terrorist organisation.
According to the Campaign to Free Barghouti, he has been subjected to various torture techniques, including sleep deprivation, position abuse(which is the tying up of detainees in painful positions for hours or days) and intimidating threats.
Despite interrogation, Barghouti's
morale remains high
That type of torture are categorically prohibited by the Universal Declaration of Human Rights (Article 5), the International Covenant on Civil and Political Rights (Article 7) and the Convention against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment.
Israel, according to the campaign, is a signatory to these key human rights covenants and therefore legally bound by their prohibitions.
Denied family access
In addition to denial to medical care, Barghouti has also been refused visits by his wife and four teenage children.
Speaking to Aljazeera.net, Fadwah Barghouti said she was very afraid for her husband.
"For one and a half years, I have not seen him. He has not seen his children. It is very difficult"
wife of Marwan Barghouti
"For one and a half years, I have not seen him. He has not seen his children. It is very difficult".
She has once again appealed to international human rights bodies to raise awareness about his situation.
Amnesty International has called for Israeli authorities to set up an independent investigation into the torture allegations, and make the results of the investigation public.
It also said those who ordered or carried out torture or other ill-treatment should be brought to justice and that Barghouti be granted regular access to his family.
The human rights body, in a report, also documented his condition, saying he has suffered "back and neck problems as a result of being tortured and otherwise ill-treated whilst being interrogated."
"Israelis must abandon the myth that it is possible to have peace and occupation at the same time, that peaceful coexistence is possible between slave and master"
During his detention, Barghouti has also carried out two one-day hunger strikes in protest at the poor conditions of detention. He has complained that his cell "is unhygienic, hot, smelly and full of insects."
According to his lawyer, Barghouti is expected to appear for sentencing in December.
But "Barghouti's morale is high, his spirit is strong and he is looking to the future", says Shkirat. His message is that "Israeli occupation will continue to be fought until independence".
Born in the village of Kobar, near Ram Allah, Barghouti joined the Fatah movement, at the age of 15, eventually becoming an elected member of its Revolutionary Council in 1989, and its Secretary-General in the occupied West Bank in 1994.
In 1996, Barghouti, who holds a BA in History and Political Studies, and an MA in International Relations, was elected to the Palestinian Legislative Council.
One of Barghouti's most oft-quoted statements is “we tried seven years of intifada without negotiations, and then seven years of negotiations without intifada; perhaps it is time to try both simultaneously.”