To obtain basic information about the regulation of the enzyme geraniol 10-hydroxylase, the behavior of this enzyme and its redox partner –the NADPH: Cyt C (P450) reductase- was examined in C. roseus hairy roots subjected to various treatments. For several of these treatments, no concerted responses of either enzyme were observed, but in general, reductase was more responsive than G10H. The possible meaning of this finding is discussed.