Symptoms of porphyria developed in a 34-year-old woman following 3 weeks of a low carbohydrate diet. Reversal of a comatose state was obtained following multiple infusions of hematin. The diagnosis of variegate porphyria was made from the pattern of quantitative urine and stool porphyrins and a plasma fluorescence that was maximal at 626 nm. This fluorescence wavelength maxima also was found in the plasma of two family members screened for latent porphyria.