If he refuses to reply, the judge will automatically register him as having pleaded "not guilty".
While a "not guilty" plea is expected, there has been much suspense in the lead-up to this second appearance about what Karadzic might say at the hearing, perhaps about his life on the run or how he expects to defend himself.
Experts believe he will exploit tactics already used by late Serbian leader Slobodan Milosevic at his UN trial and try to embarrass the United States over alleged back room deals.
They say that like Milosevic, whose own ICTY trial ended after four years with his death in March 2006, Karadzic would seek to call people like Holbrooke and the former leaders of the United States, France and Britain as witnesses.
The 63-year-old, dubbed the "Butcher of Bosnia" by some media, was arrested six weeks ago on a Belgrade bus posing as a doctor of alternative medicine, complete with large glasses and big white beard.
Trial legality challenged
In his submissions to the court so far, Karadzic has challenged the legality of his pending genocide trial and urged the UN court to order evidence from former US diplomat Richard Holbrooke about an alleged secret deal.
Declining to enter a plea immediately, he claimed Holbrooke had promised him at the end of Bosnia's bloody war that he would not face prosecution if he disappeared from the public eye.
But Holbrooke, the architect of the Dayton peace agreement that ended the war, denied cutting such a deal and described Karadzic as the "intellectual architect" behind an ideology of racial hatred in former Yugoslavia.
"Of all the evil men of the Balkans, he is the worst," he said.
Karadzic is accused of commanding the 44-month siege of Sarajevo that left 10,000 dead, and of ordering the July 1995 massacre of around 8,000 Muslim men and boys in the UN-protected area of Srebrenica.