In order to investigate the effects of plant hormones on the quantitative changes in mRNA of maize (Zea mays L.) rbcL, we used GA3, IAA, ABA and BAP. GA3 at the concentration of 10-4M resulted in decrease in rbcL gene transcript to 62%. IAA decreased the amount of rbcL transcript to about 70% at all the hormone concentrations tested. ABA did not cause a noticeable change in the amount of rbcL transcript, but BAP increased the amount of rbcL transcript to 153% at 10-8M and 123% at 10-5M, respectively. Thus, it appears that BAP is related to the increase in the amount of rbcL transcript by light.