The clinical usefulness of bone marrow scintigraphy in evaluating adult acute nonlymphocytic leukemia (ANLL) was assessed through 39 studies of 23 adult patients. Nineteen patients were in various stages of relapse and remission of ANLL and four patients were preleukemic. Results of scintigraphic studies were correlated with information concerning bone marrow status, therapy, and subsequent clinical response. When 99mTc-sulfur colloid was utilized, eight of 34 studies were normal, but in the majority of patients there was an abnormal distribution of bone marrow reticuloendothelial activity. Three of the patients with normal studies were in complete remission at the time of the normal scan. The duration of these remissions tended to be long. In four patients, 67Ga-citrate scintigraphy showed a wide variation of bone marrow uptake despite a marked increase in bone marrow myeloblasts. There was no significant correlation between scintigraphic distribution and bone marrow morphologic status nor with subsequent ability to induce a complete remission with chemotherapy. Nevertheless, these studies raise the possibility that bone marrow scintigraphy may be useful in predicting the stability of an induced complete remission in ANLL. Confirmation of this possibility must await further studies.