NOTE FROM DR. MERLE A. SANDE -What happens after an individual is infected with human immunodeficiency virus (HIV)? In how many infected individuals will infection actually progress to clinical disease? How long does this take, and how can the clinician tell that progression from asymptomatic infection to symptomatic disease is beginning? What, if anything, can be done to slow progression? These are some of the most pressing questions with which infectious diseases clinicians are faced today. Drs. George W. Ruther-ford and Alan R. Lifson of the San Francisco Department of Public Health and Dr. Harold W. Jaffe of the Centers for Disease Control have been major contributors in shedding light on these crucial questions. This AIDS Commentary comprises their collective, current thoughts on the progression of HIV infection.