A boy exhibited severe bullous skin disease a few days after birth, followed by increased fragility of the exposed skin in spring and summer. Examination at 2 1/2 years of age led to characteristic biochemical findings: increased excretion of fecal porphyrins (coproporphyrin 121 to 131 and protoporphyrin 467 to 576 nmol/g dry weight), and increased erythrocyte protoporphyrin concentration (3643 to 4840 nmol/l). Lymphocyte protoporphyrinogen oxidase activity was very low in the patient (0.4 nmol/mg protein/h) and half-normal (2.7 and 2.3 nmol/mg protein/h) in the parents, suggesting that the patient had homozygous variegate porphyria. Severe skin symptoms and a high concentration of red cell protoporphyrin concentration in an infant should prompt suspicion of homozygous acute hepatic porphyria.