This report describes a 15-year-old white boy who presented with fever, back pain, a disseminated exanthematous rash, renal failure, and hepatopathy 3 weeks after the initiation of oral minocycline therapy for facial acne. Marked peripheral and urine eosinophilia were noted. A bone marrow aspiration showed more than 50% eosinophils without any evidence of malignancy, and a simultaneous kidney biopsy showed acute interstitial nephritis (AIN). The patient's symptoms and laboratory findings improved after high-dose steroid therapy was initiated, worsened when it was withheld, and improved again after it was reinitiated in view of the biopsy findings. The patient recovered completely, and steroids were tapered to discontinuation over 3 months. Over a year later, the patient's peripheral blood mononuclear cells (PBMCs) were cultured for 2 weeks in the presence or absence of minocycline ex vivo, and minocycline was found to induce the emergence of CD4(+) cells after 1 week in culture. In conclusion, this article shows for the first time several new aspects of minocycline-induced morbidity: renal and hepatic failure can occur together, and AIN and elevated blood eosinophil counts can be accompanied by marked bone marrow eosinophilia, suggesting a systemic allergic response as the underlying pathomechanism. Furthermore, the initial phase of such a response appears to involve CD4(+) T cells detectable ex vivo. Lastly, high-dose treatment with corticosteroids appears to be beneficial in this setting.