Based on the results of a primary screening effort, a potent actinomycete isolate, MCCB 248, was selected for further studies. IC50 values were determined to the NCI-H460 human lung cancer cell line as well as to a cell line derived from normal epithelial kidney cells from the African green monkey (BS-C-1). Briefly, two fold serial dilution of the crude extract of the MCCB 248 isolate was prepared to obtain concentrations ranging from 1 mg/mL to 15.625 µg/mL in 10% DMSO; these were added to the various cell lines as described above. IC50 values were determined based on probit analysis (Brownlee et al. 1952).