We evaluated glandular-hairedMedicagospecies [perennial tetraploidM. sativaL. subsp.praefalcata(Sinskaya) C. R. Gunn, annual diploidsM. blancheanaBoiss.,M. disciformisDC, and annual tetraploids,M. rugosaDesr., andM. scutellata(L.) Mill.] for resistance to the spotted alfalfa aphid,Therioaphis maculata(Buckton), in growth chambers. Resistant and susceptible perennialM. sativaclones were used for controls. In free-choice tests, the glandular-haired species and the resistantM. sativacontrol clone were less attractive than the susceptible control clone. Very few aphids reproduced onM. disciformis. Fewer aphids were on the annuals than on the perennial glandular-haired species. When the aphids' choices were limited to the annual speciesM. scutellataandM. disciformis, they departed from both and moved around the arena. Similarly, when only the resistantM. sativaclone andM. scutellatawere available, the aphids chose the arena over the plants. In no-choice tests under three temperature regimes, resistance ofM. disciformisand the resistantM. sativaclone was similar. Resistance ofM. blancheana,M. rugosa, andM. scutellatawas similar and lower than that ofM. disciformis. Resistance of the glandular-hairedM. sativaclone was low, but rate of aphid reproduction and total nymphs produced on it were lower than on the susceptible control clone under a constant temperature of 24°C or under 29°C day-16°C night temperature regimes.