To examine the values of helper/inducer lymphocytes (T4), preoperatively, and during the chemotherapy, 1 and 3 months postoperatively in a prospective randomized study of women with cancer. The study included 30 surgically-treated patients with ovarian cancer at the Department of Obstetrics and Gynecology in Novi Sad, Yugoslavia. In the control group, 20 patients had no malignant ovarian tumor. Patients with ovarian cancer, besides surgical treatment, were treated with chemotherapy (CP protocol). Helper/inducer lymphocytes were defined by monoclonal antibody--CD4, conducted by laser flow cytometry. The average values of T4 lymphocytes in relation to control group (1.09 +/- 0.50), in IIIa, IIIb and IIIc stage of ovarian cancer decreased preoperatively (0.55 +/- 0.26), but increased in stages Ia and Ic (1.12 +/- 0.57) and in stage IV (0.31 +/- 0.51). Post surgery treatment (1 and 3 months) and during chemotherapy (CP protocol), the average values of T4 lymphocytes were lowered in relation to preoperative values.