Abstract:In previously published studies only 33–66% of the radioactivity was recovered in the urine after oral administration of14C‐histamine. In the present study the corresponding figures were higher: between 68 and 80% of the administered14C‐activity was recovered in the urine within the first 48 hours of administration. Between 1.8 and 18% was exhaled as14CO2, whereas between 13 and 19% of the administered radioactivity was excreted in the faeces. Thus nearly 100% of the administered14C‐activity was recovered. Urinary14C‐metabolites of histamine were determined by isotope dilution technique and by autoradiography. We were unable to obtain a constant specific activity for 1.4‐methylimidazole‐acetic acid by isotope dilution technique and an estimate of the balance between the urinary metabolites could not be obtained by this technique. Autoradiography indicated that oxidative deamination is the main pathway of orally administered histamine, and that imidazoleacetic acid riboside is the main urina