The aim of this study was to determine the value of haematological counts at the 4th day of a chemotherapy cycle, in order to foresee neutro and/or thrombocytopenia during the same chemotherapy cycle. One hundred and ten cycles of chemotherapeutic regimens with carboplatin (400 mg/m2, dl) and 5-fluorouracile (1 g/m2/d, by iv continuous infusion for 96 hours) every 3 weeks, were analyzed for 42 patients with locally advanced but non metastatic squamous cell carcinoma of head and neck, without prior chemotherapy. Lymphocyte counts were significantly decreased at the 4th day but normalized at the 8th day (P < 10(-6)). Decreases of lymphocyte and neutrophil counts at the 4th day were significantly correlated to grade > 2 neutropenia. The positive predictive value of lymphocyte or neutrophil counts is about 50% for some cut-off values but not high enough, with the schedule of chemotherapy in our study, to justify the systematic prophylactic therapy with haematopoietic growth factors.