PIP: A study undertaken to determine the differential effects, if any, of supply source on continuation rates of oral contraceptive usage in Mexican women. A sample of 2063 women aged 15 to 49 years was surveyed over a 6 year period ending in 1979. Of this group, 44% initially obtained the pill from the national family planning population program, 39% from pharmacies, and 17% from private physicians. Average age of users of the 3 sources differed by no more than 1/2 year; government program users tend to be less educated and private physician users to be somewhat more educated than the other women. Results show no striking differences in continuation rates among the 3 groups, and do not support the hypothesis that women who use the pill under supervision of a physician will have a higher continuation rate and lower pregnancy rates than those obtaining their oral contraceptives from other sources. In fact, a group of little educated, older, high parity rural women from among the pharmacy users show slightly higher continuation rates and probabilities of contraceptive use than any other user. In addition, there was no group of women whose contraceptive experience with the pharmacy was less favorable than the experience of women seen by a physician or the family planning program. An interaction effect between the service provider and the contraceptive user which facilitates more effective communication may be in operation across all 3 conditions. Many important questions about access to oral contraceptives, such as incidence of contraindications in users, and incidence and nature of side effects among pill users of various sources, remain unanswered. Further research is needed to clarify these issues.