Significant changes in composition of rainbow trout Oncorhynchus mykiss blood cells types were induced after 4-days exposure with mixture of Cu2+ and Zn2+ at 0.25, 0.125 and 0.06 parts of LC50 in comparison to control group. The highest concentration of metal mixture (0.25 of LC50) significantly induced elevation of the number of monocytes and poly-segmented neutrophils. Treatment with 0.125 parts of LC50 concentration increased the number of thrombocytes, monocytes and non-segmented neutrophils. The most diluted mixture resulted in significant induction of thrombocytes, monocytes, non- and poly segmented neutrophils. Analysis of leucocyte cell types in the O. mykiss blood samples after 4-days of exposure at all applied mixture parts showed signs of monocytosis and neutrophilia. Comparison of different types of leucocytes' percentages (leukogram) in fish after 4-days exposure to metal mixture and after 4, 8, and 12-days recovery periods showed that, values of neutrophils even after the 12-days recovery period at all tested parts of LC50, and monocytes after exposure with the highest (0.25) used part of LC50 were not restored to control group levels. Depuration and recovery processes in treated fish are concentration and recovery period dependent.