Standard hematologic and serum chemistry parameters were determined from 28 harp seals (Phoca groenlandica) and 20 hooded seals (Cystophora cristata) sampled from 6 March 2001 to 13 March 2001 during the breeding season. Whole blood was collected immediately postmortem from harp seal mother-pup pairs and from six hooded seal pups, and from live-captured adult hooded seals and three hooded seal pups; blood was analyzed within 24 hr at a local human hospital. A certified veterinary laboratory validated subsamples of whole blood and analyzed all serum chemistry parameters. Significant interlaboratory differences in mean values of packed cell volume (PCV) and mean cell volume (MCV) were found. Significant differences were found between samples from the five seal groups (adult male hooded seals, lactating female hooded seals, unweaned hooded seal pups; lactating female harp seals, and unweaned harp seal pups) for hematology and most serum chemistry parameters. In general, age-class influenced mean values of PCV, hemoglobin (HB), red blood cell (RBC) counts, MCV, mean cell hemoglobin (MCH), mean cell hemoglobin concentration (MCHC), and nucleated red blood cell (NRBC) counts per 100 leucocytes, but most age-related variations were species specific. Harp seal pups had significantly lower mean values of HB, PCV, MCH, and MCHC than did other seal groups, and significantly lower mean RBC counts than did hooded seal pups. Mean NRBC counts per 100 leukocytes were more than three times higher in harp seal pups than in hooded seal pups, but this difference was not statistically significant. Mean MCV were significantly lower in harp and hooded seal pups compared to those of adult harp and hooded seals. Differences in hemograms between pup species were likely because of the precocious development of hooded seal pups, which are weaned within 4 days, compared to 12 days for harp seal pups. Among adult seal groups, male hooded seals had significantly higher mean values of PCV and HB than did female harp and hooded seals, and significantly higher mean RBC counts than did adult female hooded seals. Among adult females, mean values of MCH and MCHC were statistically higher in hooded seals than in harp seals. Adult female harp and hooded seals did not differ significantly in other RBC parameters and mean leukocyte counts. Mean values of glucose, blood urea nitrogen, total bilirubin, alanine aminotransferase (ALT), alkaline phosphatase (ALP), total protein, and albumin showed species-specific variations between adults and pups. Except for ALP, few significant differences in mean enzyme activities of aspartate aminotransferase (AST), ALT, creatine kinase and gamma-glutamyltransferase were found between seal groups. Mean concentrations of electrolytes (calcium, phosphorus, sodium, potassium, chloride, magnesium, and total carbon dioxide) varied with age class, but variations in potassium and magnesium were species specific. Harp seal pups had significantly higher mean phosphorus and potassium levels compared to other seal groups.