LEPTOSPIRAL infection of white laboratory rats was first reported by Uhlenhuth and Zimmermann¹. Later it was observed in some stocks in Germany, Holland and Denmark². The infection seemed to be present inapparently in white rats, although some observers emphasized the high incidence of albuminuria in these populations. The examination of single isolated strains and the results of serological screening tests suggested Leptospira icterohaemorrhagiae as the causative agent. It was generally assumed that the infection originated from wild rats in the animal house. Human cases were regularly detected in these institutes showing mainly the picture of Weil's disease with a high fatality-rate.