A method is established for deriving ion composition from a combined ion line/plasma line incoherent scatter experiment in the ionospheric F1 region. The new method resolves the temperature/composition ambiguity in the ion line autocorrelation function by incorporating the measured plasma line offset in the least squares fitting procedure. The method has the advantage that rather short pulse lengths and integration times can be used, giving reasonably good height and time resolution. We apply the method to data from an European incoherent scatter UHF experiment carried out in July 1985 which involves an event of soft particle precipitation. The result indicates that soft energy particles depositing their energies in the F1 region tend to increase the percentage of atomic ions at these heights. ¿ American Geophysical Union 1988