Patients in the two ritonavir groups (500-mg and 200-mg dose groups) took abacavir and amprenavir for one week and then come to the clinic for blood tests to measure drug levels before taking their morning pills and at 1/2, 1, 2, 4, 8, and 12 hours after taking the medicines. They will then add ritonavir to their treatment regimen. After one week, they will return for blood tests as before. They will then add efavirenz to their regimen and had bloods drawn again after another 1 or 2 weeks.