Dacarbazine (DTIC) is a chemotherapy drug which has antitumor activity at standard doses, exhibits a steep dose-response effect in vitro, and is associated with relatively few non-hematologic toxicities. These characteristics suggest a potential role for this drug in bone marrow transplant preparative regimens. To pursue this hypothesis, 16 patients with refractory solid tumors were enrolled in a phase I study of single agent DTIC to determine the dose of DTIC requiring bone marrow reinfusion and to define the dose-limiting toxicity and maximum tolerated dose when given with autologous bone marrow rescue. Pharmacokinetics were evaluated at the 4394 mg/m2 dose level. The marrow requiring dose was 2000 mg/m2 when given as a single intravenous (i.v.) infusion. The extramyeloid dose-limiting toxicity of DTIC was hypotension, with the maximum tolerated dose of DTIC being 3380 mg/m2 when given with bone marrow transplantation (BMT). Other toxicities were transient and tolerable. At 4394 mg/m2 of DTIC, plasma concentrations declined biexponentially with a terminal half-life of 3 hours. The mean clearance was 10.6 L/hr/m2 with a volume of distribution at steady state of 37.5 L/m2 and a mean maximum plasma concentration of 150 mcg/ml. One patient with melanoma developed a partial response of short duration after receiving 2600 mg/m2 of DTIC. Dacarbazine can be significantly dose escalated with an acceptable toxicity profile, when given with BMT. Future trials should focus on the addition of this drug to current BMT preparative regimens used for the treatment of patients with lymphoma.