52 convalescent carriers of Salmonellae in = 25) and Shigellae (n = 27) were treated with a 4-week course of either co-trimoxazole or the combination pivmecillinam/pivampicillin. 84 % of the salmonella isolates and 89 % of the shigella were resistant to one or more antibiotics. Sulphonamide resistance was observed in 52 and 58 % of the strains, respectively. 12 and 44 % of the isolates, respectively, were resistant to ampicillin. All were sensitive to mecillinam and all except 2 were sensitive to co-trimoxazole. In salmonella carriers, co-trimoxazole was successful in 54% of the subjects and pivmecillinam/pivampicillin in 58%. Co-trimoxazole cured 83 % of the shigella carriers and pivmecillinam/pivampicillin 87 %. Shigella carriers responded to therapy promptly. Concurrent biliary disease or diverticulosis adversely affected the prognosis in salmonella carriers.