Serum protein determinations and total peripheral lymphocyte counts (TPLCs) were made on 61 cancer patients before and after injection of a cancer vaccine. Immunization did not significantly affect any of the serum protein concentrations. On the other hand, all patients treated with cobalt prior to immunization, were noted to have significant decrease in TPLC. Interesting results were obtained in immunized patients who did not receive prior cobalt. Postimmunization counts increased 33% over preimmune counts in patients responding to vaccine injection, but decreased 13% in patients failing to respond to the vaccine injection.