Two patients are described with constitutional hematologic abnormalities associated with pancreatic exocrine deficiency (the Shwachman syndrome). These patients, however, exhibited many features similar to other constitutional hematologic disease, such as Fanconi's anemia, which are atypical for Shwachman syndrome. These features include severe pancytopenia, markedly decreased colony forming units in culture (CFU-C), a response to corticosteroids, and leukemic transformation. A suppressor mechanism could not be demonstrated as the cause of the severe pancytopenia, based on in vitro bone marrow co-culture experiments. These patients demonstrate the extreme clinical severity which can be seen in the Shwachman syndrome, as well as the gamut of shared characteristics among the various syndromes associated with constitutional hematologic aberrations.