Results of skin and urine cultures performed by a Wellington laboratory over a selected period, were used to estimate the prevalence of common organisms and their in vitro sensitivity to chemotherapeutic agents, to determine the most efficacious and economical, anti-infective therapy. For streptococcal or mixed gram positive infections penicillin is the antibiotic of choice. For mild to moderate staphylococcal infections, erythromycin is indicated. A single dose of cotrimoxazole is economical for uncomplicated urinary tract infections, however urine culture seems warranted. Reservations are expressed regarding the assessment of in vitro sensitivity to cotrimoxazole and possible development of resistance to this agent. Ampicillin/amoxycillin is indicated for organisms resistant to sulphonamides. The need to supply doctors with information on changing sensitivity patterns of micro-organisms in the community is emphasised.