Two strains of alfalfa, one with a high and one with a low concentration of saponin in the leaves, were tested for effect on the mortality of immatureMegachile pacifica(Panzer) exposed to leaf pieces in the nests. The average difference between strains was nonsignificant.Results did not support the view that saponin in alfalfa leaf pieces used in lining the egg cell are responsible for high mortality of leafcutting bees foraging on alfalfa.