Suprathermal electron fluxes measured in the ionosphere of Mars by the retarding potential analyzer (RPA) on Viking lander 1 are presented and compared with the photoelectron flux that is produced by the absorption of the solar EUV. The calculation of the equilibrium photoelectron population on Mars is based on the multistream electron transport theory and a model neutral atmosphere and ionosphere that was actually observed by Viking lander 1. From the theoretical equilibrium photoelectron population we compute the expected RPA volt-ampere characteristic curves and compare them with those recorded by the instrument. The theoretical and the observed RPA currents below ≂170 km are in agreement, confirming that the solar EUV is the main source of suprathermal electrons at these altitudes. Above ≂170 km an additional source of suprathermal electrons is required to explain the observations. We suggest that this source is supplied by the solar wind, either by direct particle entry or by wave-particle coupling. The rate of attenuation of the topside suprathermal electron flux with altitude indicates that the ionosphere is permeated by a substantially horizontal (dip angle ≂15¿) magnetic field.