ABSTRACTInheritance of bioluminescence in North American populations ofPanellus stypticuswas analyzed using a set of five nonbioluminescent monokaryons and one bioluminescent monokaryon obtained from a basidiocarp ofP. stypticuscollected on pine wood. These were crossed with two nonbioluminescent and two bioluminescent monokaryons obtained from basidiocarps collected on hardwood in four geographically separate locations. Sexual compatibility of the geographically separate isolates indicated they were of the same biological species. Changing levels of bioluminescence intensities over time in the resulting dikaryotic cultures indicated that bioluminescence may be under stage-specific regulation. Inheritance of bioluminescence was analyzed according to the actual versus the expected maximal levels of bioluminescence intensity in dikaryons having at least one bioluminescent monokaryotic component. Bioluminescence was a dominant feature among the isolates tested. Genetic complementation groups established for dikaryons with two nonbioluminescent monokaryotic components suggested that three separate naturally occurring mutations can lead to lack of bioluminescence. Inter-allelic complementation may be involved in the expression of bioluminescence in a dikaryon resulting from a cross of two nonbioluminescent monokaryons. No significant differences among dikaryons were found in the characterization of bioluminescence emission spectra regardless of monokaryon composition.