Citric acid extracts of granule-rich fractions, prepared from rabbit and guinea pig heterophils or human neutrophils, killed Cryptococcus neoiormans in vitro. These extracts were fractionated by micropreparative electrophoresis on polyacrylamide gels. In preparations of rabbit and guinea pig heterophils, cryptococcidal activity was associated predominately with lysosomal cationic protein complex. Human neutrophils lacked strictly comparable cationic proteins but contained other components that killed C. neoformans. These components appeared to be identical to previously described proteins of the human neutrophil active against Candida parapsilosis.