We conducted a randomized crossover study comparing the hemopoietic effect of partially purified human urinary colony-stimulating factor (CSF-HU, an active drug) and human serum albumin (HSA, a control drug) in 24 patients with malignant lymphoma, solid tumors, or multiple myeloma who were receiving two consecutive courses of the same chemotherapeutic regimen. Patients received daily 2-4 X 10(6) units of CSF-HU or an equal amount of protein HSA for five days after the end of the courses of chemotherapy. Assignment to CSF-HU or HSA was determined by the envelope method. The average number of blood granulocytes of 24 cases on day 7 after chemotherapy was 2116 +/- 1649 in CSF-HU-infused courses, which was significantly higher than in HSA-infused courses (1520 +/- 1022) (p less than 0.05). The average time that patients had fewer than 2000 granulocytes/mm3 was 7.6 +/- 4.4 days in CSF-HU-infused courses and 10.3 +/- 5.0 days in HSA-infused courses (p less than 0.02). Fever greater than 38 degrees C was the most frequent side effect, occurring in 32% of the patients receiving CSF-HU infusions. A reduction in the neutropenic interval in CSF-HU-infused courses was observed in patients with fever, as well as in those without fever. Infusions of CSF-HU did not change the number of other hematological parameters, such as erythrocytes, platelets, monocytes, and lymphocytes. These results suggest that CSF-HU infusions may partially protect the patients from granulocytopenia after anticancer chemotherapy.