-The influence of different diets on the haemolymph of adult honeybee workers was examined. The laboratory experiments took place in early summer. There were three experimental groups fed with one of the following diets: pollen with sugar, pollen substitute alone, or sugar. A sample of haemolymph was taken from 7-8 day old bees and numbers of haemocytes of each type (plasmatocytes, granular haemocytes, and other types of haemocytes pooled together) were recorded and the metabolic activity of haemocytes was observed. A lack of protein caused a significant increase in the percentage of granular haemocytes, a significant decrease of other types and a lower metabolic activity. The examined pollen substitute caused a decrease of total haemocyte count. The decrease in the metabolic activity of haemocytes was lower than without protein.Apis mellifera / diet / haemocyte / adult worker