The time evolution of the very large solar particle event occurring on days 82--90 (March 23--31), 1991, as measured at 2.5 AU by the instrumentation on the Ulysses spacecraft was quite complex. Measurements by the HI-SCALE instrument of the nuclear composition (emphasizing Z≥6) of the interplanetary particles at a time resolution of two hours provides information on the different interplanetary regions which swept over the spacecraft. The Fe/O abundance ratio is found to differ slightly in the regions before and after two tangential discontinuities. The Fe/O abundance ratio is also found to depend strongly on the energy/nucleon of the particle, with values of ~0.7 for energies of ~0.5--1.0 MeV/nucl. to values of ~0.2 for energies ~8--16 MeV/nucl. ¿ American Geophysical Union 1992