In 1984-1994 black-headed gulls (Larus ridibundus) from various localities in the Czech Republic were examined to assess the incidence of salmonellae. A total of 99 eggs from two nest colonies were examined. No salmonellae were detected. In examinations of 740 young birds from three colonies the total prevalence was 19.3%. In full grown gulls (number of examined birds 189) from five localities the total prevalence of salmonellae was 4.2%. In water specimens near the nest colonies, other habitats of the gulls and from soil specimens from one nest colony (throughout the year) salmonellae of the same serotypes as in gulls were isolated. The young birds contaminate surface waters with salmonellae. The importance of adult birds as a source of infection is much smaller. Only for the young of aquatic birds (fowl or free living) gulls could be an important source of salmonella infections. The presence of salmonellae in gulls is due to contamination of surface waters and the surroundings of nest colonies with salmonellae.