Sensitivity to diphtheria toxin as a species-specific marker in hybrid cells.

INTRODUCTION It is known that cells from different animal species show marked differences in their susceptibility to the destructive action of diphtheria toxin (Lennox & Kaplan, 1957). It therefore seemed possible that diphtheria toxin might be used as a speciesspecific marker in the study of interspecific hybrid cells and perhaps also as a selective agent to facilitate the isolation of such hybrids from fused cell populations. The investigation described in the present paper explores these possibilities.