Adriamycin (ADM) concentrations in neoplastic plasma cells, nucleated blood cells, bone marrow cells, and plasma were measured in seven patients with advanced multiple myeloma. ADM was administered as a 96-hour infusion of 9 mg/m2/24 hr. Maximum plasma ADM concentrations were 15.8 +/- 4.4 ng/ml. ADM concentrations in nucleated blood cells, bone marrow cells, and plasma cells increased continuously throughout the 96-hour infusion. Maximum cellular levels were up to 200-fold higher than the maximum plasma concentration and were similar to levels observed shortly after administration of the total dose in one rapid injection. The cellular AUC for 96-hour infusion and bolus injection were comparable. Thus continuous infusion is the equivalent of bolus injection in delivering ADM to the target cells in bone marrow, although plasma ADM concentrations remained very low. These results provide support for administering ADM as a continuous infusion with less toxicity and better patient tolerance.