Fifty patients were treated for suspected serious bacterial infection with Timentin 3.2 g 6-8-hourly. Three patients did not complete a minimum of 48 h treatment. Pathogens were isolated from 28 of the remaining 47 patients; 13 were resistant to ticarcillin but fully sensitive to Timentin; six of these isolates were Staphylococcus aureus. Five of the patients with Timentin-sensitive organisms or no significant growth failed to respond or relapsed after Timentin but also failed on subsequent therapy. An additional patient relapsed because of inadequate duration of treatment and one patient, with salmonella enteritis, became an asymptomatic carrier. The Timentin-resistant organisms were a Pseudomonas aeruginosa which responded to ceftazidime, a Klebsiella pneumoniae which was of doubtful clinical significance and an Escherichia coli which caused a relapse of pyelonephritis 16 days after apparently successful treatment with Timentin. No serious adverse reactions were seen. Timentin was effective against ticarcillin-resistant organisms but its final role will depend on the prevalence and significance of in-vitro resistance to the combination amongst Enterobacteriaceae and pseudomonads.