Investigations were made of 2-(nicotinoylaminoethanesulfonylamino)pyridine (NTP), a new compound with anti-ulcer effects, to clarify the relationship between its biotransformation and pharmacological effects. The effect of NTP was investigated by using two types of experimental gastric ulcer models in rats. The anti-ulcer effect was revealed to be an action of NTP itself. In order to study the biotransformation of NTP, a quantitative analysis method by HPLC was established. When NTP was orally administered to rabbits, 2-(aminoethanesulfonylamino)pyridine (TP), which is a metabolite of NTP, appeared in plasma and lymph. When NTP was orally administered to rabbits to investigate its distribution in organs, a massive amount of NTP and TP appeared in various organs within 7 hr after administration. We conclude that the pharmacological effect of NTP appears to be associated mainly with the unchanged substance.