The efficacy of several types of contraceptive methods was tested in an area of approximately 20 square miles, located 25 miles from San Juan, Puerto Rico. Populations in 1950 were 13,605 urban and 1080 rural in the test area. The maternal-health clinic, operated by the Commonwealth Health Department, employed a nursing staff of 5 plus a "jeep" and driver. Two clinics per week were held for patients living in the urban area and weekly visits by a nurse were made to rural homes. The Health Department provide adequate supplies of diaphragms, condoms, suppositories, and contraceptive creams and jellies (to be used either with a diaphragm or injected by syringe). The nurse was prepared to give instructions in the rhythm method to patients having religious objections to mechanical methods, but no request for such instruction was made. Patients were 1st offered diaphragm and jelly, jelly with 5 ml applicator, suppository, or foam tablet, but condoms were also supplied if requested. A change in method was allowed whenever requested. Age-specific, unplanned pregnancy rates following registration with the clinic were compared with rates among women not practicing contraception prior to registration. For age groups below 35 years, the unplanned pregnancy rate was between 40 and 50% of the level of fertility record prior to use of contraceptives. Reasons for 85 unplanned pregnancies of patients using contracetive methods include noncooperation of the husband, occasional failure to use the available method, and failure to use method because of fear of pain. Only 9% of unplanned pregnancies were thought to be dependent on incorrect use of the method. The authors conclude that at present the most acceptable contraceptive technique in a rural area of Puerto Rico is the condom. Home visits by a nurse in rural areas provide the most effective way of disseminating birth control education.