The aim of this study was to determine the haematological effects of 1 g methylprednisolone given intravenously as pulse steroid therapy (PST) to 10 cancer patients who had not received any chemotherapy or immunoactive drugs in the previous 3 weeks. Haematological values as determined with flow cytometry were evaluated before, and I and 24 h after, the pulse therapy. Total leucocyte count was found to be decreased at the first hour and significantly increased at the 24th hour, whereas total lymphocyte count decreased at the first hour and remained low at 24h. CD4 lymphocytes were found decreased al the first hour whereas CD8 lymphocytes were significantly decreased at the 24th hour. The CD4/CD8 lymphocyte ratio and the values of haematocrit and platelets did not change significantly. The decrease in the total leucocyte count after 1 hour of steroid administration was notable, in addition to the results which were in accordance with previously reported data about steroid effects on haematological values.