AbstractThe aliphatic diamine putrescine, a metabolic precursor of the polyamines spermidine and spermine, markedly stimulated the growth of a murine lymphoblastoid cell line (R 1.1) infected withMycoplasma orale, under conditions of arginine limitation. The diamine acted by suppressing the growth of the mycoplasma, which use arginine as a major energy source, and thereby prevented the depletion of arginine from the medium. The antimycoplasmal effects of putrescine occurred at concentrations that were neither stimulatory nor toxic to uninfected cells.