Researchers in the fields of cocaine abuse and circadian locomotor activity probably do not often collaborate, but a paper published in the 13 August Science, by Jay Hirsh and colleagues, has established a link between the two. Hirsch's group demonstrated that four of the five known circadian rhythm genes are also necessary for cocaine sensitization—the heightened response to small doses of cocaine thought to underlie its potential for abuse. Wild-type Drosophila demonstrate sensitization to cocaine in the form of exaggerated grooming, proboscis extension and circling locomotor behaviors. However, this sensitization is eliminated in flies mutant for the recently identified circadian genes period, clock, cycle and doubletime, even when higher doses of cocaine are given over two days. Hirsch's group believes that the link between cocaine sensitization and circadian control of locomotion may occur at the level of dopaminergic signaling pathways (see also Koob and Caine, page 993). Although it is difficult at this stage to extrapolate this discovery to human drug addiction or circadian rhythmicity, these unexpected findings bear serious consideration because of the conservation of the biogenic amine and circadian pathways between drosophila and humans.