For the second time within a week, a man has died in pretrial detention, the BBC Russian Service reported on Wednesday.
Oleg Golobokov, 46, was being held on suspicion of violating copyright laws when he died of an epileptic seizure on Tuesday.
Another detainee, Andrei Kudoyarov, 48, died after suffering an apparent heart attack.
"This is becoming an epidemic. Something needs to be done urgently," veteran human rights activist Lyudmila Alexeyeva said, Interfax reported on Wednesday.
Police have opened a criminal investigation into Kudoyarov's death and an inquiry into Golobokov's death.