A semiautomatic electronic blood cell counter (Sysmex F-800:Toa Medical Electronics Europa Gmbh, Hamburg, Germany) was evaluated using canine and feline blood, following the International Committee for Standardization in Hematology protocol (ICSH, 1984). Precision and overall reproducibility were acceptable for all the parameters studied except for the feline platelet count, in which overlapping of erythrocyte and platelet populations prohibited determination of an accurate platelet count. Since carry-over from canine hematocrit values and platelet counts and from feline hematocrit values was unsatisfactory, the use of a blank diluent sample between different analyses was necessary. Linearity of the analyzer was acceptable in the studied range. Thirty canine and feline blood samples were analyzed using the Sysmex F-800 and a manual method. Correlations between both methods were acceptable for all the parameters, except for feline platelet count and erythrocyte indices for both species. In the storage study, red blood cell count and hemoglobin concentration were the parameters with the longest stability (72 hours at 4 degrees C and 25 degrees C) in both species. A statistically significant increase in MCV was obtained at 12 hours post-extraction in canine samples stored at 25 degrees C and at 24 hours in refrigerated samples. Feline leucocyte counts showed a downward trend at 12 hours post-extraction at both temperatures. Canine platelet count decreased significantly at 6 hours post-extraction in samples stored at 4 degrees C. During the evaluation period, Sysmex F-800 was user friendly and appeared well suited for routine canine and feline blood cell analysis.