Among 291 persons of all age groups from Cologne or Frankfurt and environs who had been in contact with golden hamsters there were 17 (5.8%) with neutralizing antibodies against lymphocytic choriomeningitis (LCM), while such antibodies were present in only 5 (2%) of 251 persons without such contact, the difference between antibody rates representing a probability of error of 5% LCM-virus infections caused by golden hamsters occurred also in city dwellers, younger age groups and more females than has been previously the case, confirming an increased risk through contact with pet hamsters. Because of the danger of intra-uterine damage in case of infection, pregnant women had best avoid all contact with hamsters.