Bioluminescence in Pyrocystis lunula depends on circadian movement of scintillons and chloroplasts between active and inactive locations. The involvement of the cytoskeleton in these transport processes was investigated using cytoskeleton-specific drugs. Chloroplast movements were visualized by chlorophyll autofluorescence and confocal scanning laser microscopy. Latrunculin B and Oryzalin prevented translocation of chloroplasts. Four hours after transition to the night phase, mechanically inducible bioluminescence was inhibited by Latrunculin B, the myosin inhibitor 2,3 butanedione monoxime, and Oryzalin in dose-dependent fashions. The actin stabilizer Jasplakinolide slightly enhanced bioluminescence but eliminated Latrunculin B effects. The microtubule depolymerizer Colchicine had no effect on bioluminescence. These results suggest that F-actin and microtubules are involved in the movements of chloroplasts and scintillons. Although the drugs tested affected bioluminescence, further experiments are needed to determine whether effects on bioluminescence were mediated by drug-induced failed translocations of scintillons or chloroplasts.