During 1990 and 1991, 380 faecal samples were collected from horses with diarrhoea. Sixty-nine (18 per cent) of the samples yielded a positive culture for Salmonella species, and salmonellae were cultured directly from 37 (54 per cent) of these cases. In 32 (46 per cent) of the cases the salmonellae were found after culturing the organism in an enrichment medium. Salmonella typhimurium was isolated from 43 samples, S hadar from three samples, S arizona from two, S enteritidis from two, S virchow from one, S blockley from one and S bareilly from one sample. In 1990, S typhimurium phage type 200 was the predominant phage type, whereas in 1991 phage types 510, 656 and 658 were encountered most often. The antibiotic susceptibility of 53 of the 69 isolates was assessed and 28 of them were resistant to more than three antimicrobial agents. Resistance to streptomycin and the tetracyclines was common, but most of the isolates were sensitive to gentamicin and nitrofurantoin.