An adaptive least-squares (ALS) classification which is capable of relating structure to activity rating of chemical compounds has been developed. The ALS method makes decisions for multicategory pattern classification by a single discriminant function. For the set of 16 mitomycin derivatives belonging to five activity classes used in this study, the present method is shown to be efficacious compared to other classification procedures such as the simple least-squares method, the Rao-type discriminant analysis, and the K-nearest neighbor method.