People who joined Matrix House, an autonomous self-help group at the Lexington, Kentucky, Federal Narcotics Hospital, tended to be dissimilar to a white “street” addict on a number of variables. Proportionately, they came from a higher socio-economic background; they were more often young, white, and single males; they were inclined toward “less complicated” kinds of crime while on the streets; they were less criminally oriented in that they had fewer arrests and spent less time incarcerated; they had somewhat shorter addiction careers; and finally they abused different types of drugs, primarily psychedelics. Overall, the Stayers seemed to differ from a sample of 267 STs (other Lexington patients) and the Leavers were more similar to the STs, which may partially account for the fact they left Matrix House. The main point derived from this study is that Matrix House, as a self-help modality which could have drawn its members from a fairly representative population of narcotics addicts, attracted only a certain type, as indicated above. It tended to choose people who had similar characteristics, or perhaps conversely, only a certain type of individual chose this self-help modality. Unfortunately, whatever the characteristics of an individual who entered this treatment modality, on the average he only remained a short five months.