A series of mainly marine derived natural products were tested for their activities against Mycobacterium tuberculosis and M. avium. Of the thirty-nine compounds tested fifteen demonstrated minimum inhibition concentrations (MICs) of 32 micrograms/ml or less, and eleven had MICs of 16 micrograms/ml or less. The most active compound found in this study was the sponge derived metabolite axisonitrile-3 (MIC 2 micrograms/ml).