Eighty cultures of thermophilic actinomycetes isolated from Bombay soils were screened for lytic action on heat-killed cells of six test bacteria. The majority possessed lytic properties of varying degrees. Gram-negative bacteria were far more susceptible than gram-positive ones. Acetone-precipitated lytic enzyme systems of two cultures — A 29 (Thermomonospora fusca) and A 60 (Thermoactinomyces vulgaris) proved stable at 70 C for 4 1/2 hr and at 80 C for 50 min but were destroyed in 10 min at 100 C. Optimum activity was at 70 C and at pH 9.0. Lytic enzyme systems from both these cultures partly hydrolysed casein and rapidly liquefied gelatin.