Agencies which enforce safety, pollution, fraud, and tax laws prosecute very rarely; other enforcement methods are used which are comparable with police cautions. Consequently, working class crime is prosecuted frequently while middle class crime is not. This article compares prosecution practices in the police and the Factory Inspectorate by drawing on recent E.S.R.C.-financed research on police prosecutions. It concludes by evaluating various justifications and explanations for those differences. Class bias is not deliberate. Rather, it is a product of considerations that are inevitably influential in a capitalist society. (Author abstract)