Blood counts were performed on 100 male and 100 female staff to establish normal ranges for our hospital. Neutrophil counts were found to be on average 0.66 times 10-9/1 (660/mm-3) higher in women than in men. Statistically this difference was highly significant and was not due to the fact that many of the women were taking oral contraceptives. The neutrophil counts of the men and women were also on average 0.50 times 10-9/1 (500/mm-3) greater in the afternoon than in the morning. A correlation was observed between the neutrpphil and the monocyte counts.