The methodology of recursive partition and amalgamation in biostatistics is presented and a FORTRAN program for its implementation, RECPAM, is described. RECPAM can be used to obtain classifications of patients according to several criteria commonly occurring in clinical biostatistics: an example is prognostic classification based on survival data. Classes are defined by simple statements, expressed in clinical terms, about predictor variables (e.g. prognostic factors). Special features of RECPAM are: the possibility of implementing a variety of classification criteria, the integration of recursive partition and amalgamation, and the availability of several strategies for constructing classification trees. A simple example to illustrate input and output features is given. The scope and flexibility of RECPAM will be illustrated in greater detail in a subsequent paper.