Extrusion has been conducted on five Cu–P alloys. The effects of extrusion temperature, strain rate, and extrusion ratio on the pressure required to initiate the process are considered. Attention is given to the problem of hot shortness to which Cu–1.5P is particularly susceptible. Although the second phase Cu3P is brittle at room temperature, evidence is given that under hot-working conditions it exhibits extreme plasticity and a low deformation resistance. It is shown that for all alloys the maximum pressure can be satisfactorily correlated with a function of extrusion parameters. Based on the established relations and estimates of temperature changes, extrusion limits can be determined.MST/49