Variegate porphyria (VP) is a dominantly inherited acute hepatic porphyria characterized by a 50% decrease in activity of protoporphyrinogen oxidase (PO) which catalyses the last step of heme biosynthesis. In VP families, most of the gene carriers are asymptomatic but at risk of developing acute attacks if subjected to precipitating factors. Recognition of the carrier status is the first step of an efficient preventive care. This could be achieved by measurement of PO activity which is a sensitive and specific but tedious method. A specific plasma fluorometric emission at 626 nm has been shown in VP patients. Here we show that this simple and inexpensive method is specific but poorly sensitive, especially in detection of asymptomatic carriers. We conclude that this procedure should not replace PO activity measurement in VP family studies.