Isolated erythroid hypoplasia and renal insufficiency induced by long-term griseofulvin therapy. We describe a patient with hematuria, pyuria, eosinophiluria, decreased renal function, and severe anemia that developed while she was receiving chronic therapy with griseofulvin for onychomycosis. We offer evidence that griseofulvin can cause an isolated erythroid hypoplasia and possibly an allergic interstitial nephritis. This is the first documented case of the above entities induced by the agent. We would recommend, based on our report, that otherwise healthy patients, when maintained on the drug for extended periods of time, have periodic determinations of renal function and hematologic status. As drug-induced erythroid hypoplasia typically occurs after a relatively long period of dosing, it may be prudent in certain individuals to monitor the CBC at approximately bimonthly intervals after initiation of therapy. Recommendations regarding monitoring of renal function are more difficult, as acute allergic interstitial nephritis can occur after either short- or long-term exposure to certain drugs. 