A FORTRAN program PRSTRC has been developed for protein secondary structure prediction, which is a modified Chou and Fasman (1978) analysis. This implementation carries out a running average of amino acid structure occurrence frequencies, utilizes a simple set of nucleation conditions, and allows user control over nucleation threshold and cutoff parameters. The algorithm includes prediction of the newly defined secondary structure elements: omega loops (1986). It also generates a charge distribution and hydropathy profile. Output includes a simple graphic display for a printer, or a CRT using color addition. Correct structures are predicted for T. dyscritum hemerythrin and the variable domain of mouse immunoglobin k-chain.