The total number of cases that the Antitrust Division has filed during the past decade has increased, but the number of significant criminal price-fixing cases has declined. Policy changes have had significant effects on other areas of enforcement. This paper argues, however, that the decline in this dimension of antitrust enforcement can be explained by a 1974 act of Congress that increased criminal penalties for price-fixing violations from the misdemeanor level to the felony level. According to this argument, the stiffer penalties' deterrent impact has reduced the supply of antitrust violations. In this respect, the analysis highlights the flaws in measuring the strength of enforcement from the frequency of cases filed. In addition, the paper reports empirical evidence from a multinomial logit model of defendant plea choice indicating that the felony penalties encourage defendants to plead not guilty more frequently. Furthermore, data on the outcomes of criminal antitrust cases reveal that the government has greater difficulty in obtaining convictions when felony penalties apply. From the viewpoint of enforcers, these findings imply that detecting and prosecuting significant price-fixing violations is more difficult. This, in turn, helps explain the reduction in related private enforcement. Copyright 1989 Western Economic Association International.