Data were collected via interviews, observations, and analysis of ASAP status reports prepared for the National highway Traffic Safety Administration. Puerto Rico's new law combined punishement with rehabilitation. It called for presentence investigations to determine whether offenders were problem drinkers or social drinkers and allowed judges to isue restricted licenses until offenders participated in rehabilitation or education programs. The blood alcohol concentation law was changed to establish breath testing as the preferred method of determining intoxication, but it left the intoxication level at 0.15 percent. The new law and stronger enforcement efforts increased the number of problem drinkers identified from 221 in 1973 to 1,146 in 1974. In addition, judges gradually came to rely on presentencing investigators and probation officers for advice on how to treat drunk driving cases. Nevertheless, the law's emphasis on the breath test resulted in dismissal of cases in which experts were unavailable to testify on the accuracy of testing equipment. Moreover, judges remained lenient with defendants who refused to take a test. A 1975 law revision set the intoxication level at 0.10 percent, but its other changes created major administrative problems. Results supported the hypotheses that legislation alone cannot bring about changes necessary to improve handling of drunk driving cases and that the maximum penalties are rarely used. In addition, judges are unlikely to suspend or revoke licenses if they believe doing so will cause hardship to defendants and their families. Figures, tables, and appendixes presenting additional data and a list of 17 references are included. (Author abstract modified)