The effects of prestorage leukoreduction and storage duration on the in vitro quality parameters of canine packed red blood cells (pRBCs) stored in saline-adenine-glucose-mannitol (SAGM) were investigated. Hematological, biochemical, and morphological changes in filtered and unfiltered pRBCs were determined each week during 42 days of storage. All of the parameters changed significantly during storage. The effects of leukoreduction on leukocyte and erythrocyte count, packed cell volume, hemoglobin content, and erythrocyte morphology were significant. While supernatant K increased during storage, glucose, Cl, and 2,3-diphosphoglycerate (2,3-DPG) concentrations decreased. Filtered pRBCs had higher 2,3-DPG levels throughout storage than their unfiltered counterparts. It was concluded that the leukoreduction filter significantly decreases the number of leukocytes and that canine pRBCs can be stored in SAGM for 42 days. Furthermore, leukoreduction may be a consideration with the intention of improving oxygen delivery, since the filtered pRBCs had a higher 2,3-DPG concentration.