Two residential programs for dually diagnosed (severely mentally ill and substance abusing) homeless individuals in Philadelphia were compared in a quasi-experimental field study. Findings indicate that the experimental model, a hybrid psychosocial and drug rehabilitation program, did significantly better in maintaining clients in care and in successful rehabilitation than the comparison model, a modified therapeutic community program. However, the overall rate of success in both programs was quite modest. We found Emile Durkheim's concepts of organic and mechanical solidarity to be useful in comparing the structure of the two programs. Because of the small number of clients treated by these programs and the unique characteristics (predominantly young, black and male) of this urban population, findings are not conclusive but clarify direction for further practice and study.