Wan Yanhai, China's most prominent AIDS activist, knows the importance of staying in touch. So on Aug. 24 when he stopped answering his cell phone, his wife was immediately alarmed. A week later, Wan is still missing. Human rights groups say he may have been arrested in Beijing for speaking out about China's growing AIDS crisis. The Shanghai-trained doctor has run afoul of authorities before, most recently in July when his Beijing-based AIDS Action Project was stripped of its legal status and forced to vacate its offices on a research institute campus. But if Wan has been picked up, who's got him? On the day he vanished, Wan attended a film screening at the Beijing gay bar On/Off; a friend noticed three men with walkie-talkies watching him. But police at the Beijing Public Security Bureau say they don't know where he is. (The bureau is required by law to notify detainees' families within 24 hours.) 'There were definitely people who wanted him to shut up,' says fellow activist Hu Jia. 'But for now, we're just not clear why he has disappeared.' All anyone can do is wait for his call.