The present study was undertaken in an attempt to establish whether or not some of the many biochemical effects of cannabinoids could be explained by inhibition of energy generation. Of particular interest was the relationship of inhibition of DNA synthesis in L1210 murine leukemia cells by certain cannabinoids to possible effects on respiration. In studies using these cells, delta9-tetrahydrocannabinol (delta9-THC) and delta8-tetrahydrocannabinol (delta8-THC) were inactive when tested both in vitro and in vivo. Since these cannabinoids have previously been shown to be inhibitors of DNA synthesis in L1210 cells, there is no necessary relationship between inhibition of the two processes.