The computer program COSMAP for construction of circular restriction maps has been developed. The generator is based on a permutational algorithm that puts forward all the possible maps that can be made with two enzymes, and the consistency checker compares the calculated and experimental double-digest fragment sizes within a predefined error bound. The output consists of the complete set of solutions ordered by a score number that is based on the matching degree between experimental and calculated double restriction fragment sizes. The program allows the application of heuristic rules which reduces the number of permutations to be checked and the number of sound solutions.