Article abstract Hematologic complications secondary to diphenylhydantoin therapy generally have been considered to be unusual hypersensitivity or idiosyncratic reactions on an im-munologic basis. This paper reports a case of a diphenylhydantoin-induced blood dyscrasia manifested by panrnyeloid hypoplasia. The dose-dependent toxicity was reproducible and a function of elevated diphenylhydantoin serum levels, suggesting the possibility of a direct toxic effect.