In the last 10 years, there has been general agreement that niclosamide (bayluscide) is the preferred molluscicide for control of the snails transmitting Schistosoma mansoni and Schistosoma haematobium. This chemical has been widely tested in pilot projects and is in use in expanded control projects in Brazil, Puerto Rico, Egypt, Iran, and other countries. A comparison of the results from six pilot projects in these countries was analyzed with particular attention to the costs of the programs, since the benefits were fairly similar in terms of rapid snail control. It was shown that costs were generally related to simple geographic parameters such as volume of snail habitat and distance between habitats. The annual costs in 1972 prices ranged from a minimum of US $1 per 100 m3 of snail habitat treated for dry regions with large irrigation systems, to a maximum of US $40 per 100 m3 treated in areas of high rainfall with only a few scattered, natural waterbodies. Use of the reported data for estimating the cost of current programs was demonstrated by projecting costs for Puerto Rico and the Sudan in 1978 prices.