Both free and sessile haemocyte counts in Alphitobius piceus showed wide variations between 06.00 and 22.00 hr. Variations in the haemogram appeared to be related to sex related cycles of activity, presumably with special reference to feeding patterns. Males showed higher total haemocyte counts during the day in comparison to females. In both sexes, the percentage of prohaemocytes and spherule cells and only in males, plasmatocytes increased during the early hours of night. In females, the percentage of granular haemocytes decreased notably between 18.00 and 20.00 hr. Number of adipohaemocytes and oenocytoids did not vary significantly. Heat treatment caused release of sessile haemocytes into the circulation resulting in a notable increase in total haemocyte counts during the day. This increase was comparatively high in females in comparison with males. Altered photoperiod had little effect on these haemocyte variations. Blood volume was slightly higher in the night than in the day in both sexes. The variation of blood volume was insignificant under both heat treatment and altered photoperiod conditions.