The radiation-induced swelling of simple Fe-Cr-Ni austenitic alloys is known to be very sensitive to solute additions. It is shown in this paper that three of the most common solute elements (P,Si,Mo) exert a very complex and often non-monotonic influence on swelling with increasing solute level. The complexity of this influence and its dependence on other variables appears to be the result of a closely balanced competition between two or more roles played by each solute in its interaction with both vacancies and interstitials. This competition yields a variety of different swelling behaviors in response to changes in solute or solvent composition, displacement rate, and irradiation temperature.