A straightforward method was designed for mapping the order of DNA restriction fragments obtained by a double and two single digestions, without the necessity of using a computer or a radioactive label. All possible solutions compatible with a pre-set level of error in the determination of sequence lengths are obtained. The primary assumptions are given, and the appropriate modifications of the algorithm are presented as a function of any assumptions one is unable (or unwilling) to make. Use of the method in connection with end-labeled fragments is also described.