Between March 16 and April 25, 1981, sixteen neonatal harbor seals, with estimated ages of less than 7 days, were admitted to the California Marine Mammal Rehabilitation Center. The pups were weak and in many cases retained the lanugo or partial lanugo coat normally shed in utero. Leukopenia was a consistent laboratory finding.  Many animals had either icteric mucous membranes on physical examination or increased serum bilirubin levels. Death occurred in 14 out of 16 animals.  Terminal signs included cyanosis, respiratory distress and coma.  Necropsies routinely revealed "wet" lungs, but no other gross findings. Histopathology showed pulmonary edema and congestion, but no causative agents were identifiable. Diagnostics in 1982 included routine CBCs and chemistries; with added information on cortisol levels, T3, T4 and immunological status of these pups. Differential diagnoses are: Respiratory Distress Syndrome, Immunodeficiency, Lipid Metabolism Defects, Congenital Heart Failure, and Stress.