Seventy-nine adult patients with acute nonlymphoblastic leukemia (ANLL) were treated on the L-6 protocol at Memorial Sloan-Kettering Cancer Center between May 1970 and January 1974. Forty-two patients achieved a complete remission (CR) and nine of these are still disease free, with a minimum of seven years of follow-up. An extensive statistical analysis has been carried out on a large number of pretreatment and treatment characteristics to identify factors related to CR and remission duration. Multivariate regression techniques yielded as favorable characteristics associated with CR, in order of importance: young age at diagnosis, the presence of Auer rods at diagnosis, and treatment with Pseudomonas vaccine. A regression model for remission duration identified as favorable prognostic factors for long-term remission: at most two courses of induction therapy, an intermediate age range, and a low platelet count at diagnosis.