The tolerability of tablets containing the ampicillin esters, pivampicillin and bacampicillin were compared clinically in 138 patients and by gastroscopy in 2 healthy volunteers. The clinical study showed no difference in tolerability, 26% of patients taking pivampicillin and 23% of those taking bacampicillin reported side-effects. Both preparations were equally effective clinically: 94% of patients taking pivampicillin and 91% of those taking bacampicillin were cured or improved. Gastroscopy showed that the pivampicillin tablets disintegrated more rapidly (10 minutes) than bacampicillin tablets (36 minutes). After disintegration, the pivampicillin tablets covered a larger area of the gastric mucosa than did tablets of bacampicillin.