The goal of this study was to determine whether actinomycetes isolated from a volcanic cave in western Canada could produce novel antimicrobial compounds against six multidrugresistant pathogens when exposed to UV light. One hundred and seventy-six actinomycete strains isolated from Helmcken Falls Cave, Wells Gray Provincial Park, BC, were screened against six pathogens using the “plug assay” in UV light and no light conditions. Of the 176 strains tested, 100 or 57% of the cave actinomycete strains had antimicrobial activities against the pathogens in 124 different instances: 35 instances when exposed to UV and no light, 30 when exposed to UV light, and 59 instances when exposed to no light. The metabolites of six actinomycete strains also lost their antimicrobial activities when exposed to UV light. While the metabolites produced by these strains have yet to be determined, exposure to lighted environments may either deactivate or enhance the antimicrobial activities of cave actinomycete strains. This study represents a confirmation that cave actinomycetes are potential sources of novel antimicrobial compounds and also is the first report of the enhancement of antimicrobial activities of some cave bacteria by exposure to UV light. Further investigation of the role of UV light with respect to activation/deactivation of antimicrobial activities of cave actinomycetes is required.