A study was carried out to compare the sensitivity as well as cost of three different methods of psychiatric case detection. It was found that the simplest method, which involved interviewing about 3% of the adult population, with a questionnaire taking only five minutes to complete, picked up as many adult epileptics and nearly as many psychotics as the inquiry with all the adults in the population using a sophisticated structured interview schedule. A method of medium complexity, in which the short five-minute questionnaire was given to one adult member of each family, detected in addition to all adult epileptics and psychotics, and many juvenile epileptics and mentally retarded. The cost of the simplest method was one-ninth and that of the method of medium complexity, one-fifth of the cost of the most sophisticated method. The method of medium complexity is recommended for use in the rural psychiatry programme of the developing countries.