The aim of this study was to assess the effects of a sublethal dose (1.6 mg/l) of DDVP (dichlor- vos) on hematological parameters of rainbow trout (Oncorhynchus mykiss) after 28 days of exposure. The DDVP caused increases in the red and white blood cell counts, hemoglobin, ery- throcyte sedimentation rate, mean corpuscular volume, and mean corpuscular hemoglobin con- centration (MCHC). On the other hand, it decreased thrombocyte (Plt), hematocrit (packed cell volume), and mean corpuscular volume. The only statistically significant differences between exposed and unexposed fish were in white blood cell count and MCHC