Faiq Mohammed Ahmed told the court he was working at a Kurdish militia hospital in 1987 when victims of gas attacks were brought in.
"The patient's eyes were tearing up and his face was red and he had difficulty breathing," said the doctor, adding that the patient was effectively blind and had to be helped into the examination room.
"After diagnosing the patient, I knew the man had been hit with mustard gas."
"I saw a woman lying on her face near a stream... I discovered she was my mother. I wanted to kiss her, but I knew I could be infected by the chemicals"
Abdel Qader Abdullah
Law and disorder
The trial, which began on August 21, has heard more than 70 witnesses, mostly victims of the brutal Iraqi campaign that swept through the country's Kurdish provinces at the end of its war with Iran in 1988.
Saddam and his six co-defendants are accused of killing 182,000 Kurds when government troops suppressed a Kurdish uprising with artillery, air strikes and poison gas attacks.
On Monday, the court heard a testimony from Abdel Qader Abdullah, a former Kurdish fighter who lost 22 members of his family in a gas attack.
"I saw a woman lying on her face near a stream," he said. "When I turned her over I discovered she was my mother. I wanted to kiss her, but I knew I could be infected by the chemicals".
Saddam has already been sentenced to death for his role in the execution of 148 Shias from the village of Dujail in revenge for an assassination attempt in 1982.
Nuri al-Maliki, the Iraqi prime minister, has said he expects Saddam to be hanged before the end of the year.
Another day of killings
Meanwhile, eight people have been killed and 40 others wounded when a series of mortar bombs exploded in a central Baghdad market.
Four people, including two women, were killed when a suicide bomber blew himself up on a bus travelling through Sadr City. Another 12 were wounded in the attack.
Another four people have been killed when a bomb went off in a shop near a bus station in the town of Iskandiriyah, south of Baghdad, police said.
In western Baghdad's upscale Mansur district, armed men attempted to assassinate Brigadier-General Mohsen Qassim, the head of the security force of Iraq's Sunni-controlled ministry of higher education, but only killed his driver.
The attacks come a few hours before a report from a bipartisan US panel that will recommend new tactics for curbing bloodshed in the country.