Several features of the molecular circadian oscillator of the chicken pineal gland show homology with those in the mammalian SCN. Studies have shown the effects of PACAP on the mammalian SCN, but its effects on the expression of clock genes in the avian pineal gland have not yet been demonstrated. Clock and Cry1 expression was analyzed in pineal glands of chicken embryos after exposure to PACAP-38 in vitro. PACAP reduced expression of both clock genes within 2h. Ten hours after exposure, mRNA contents exceeded that of the controls. Our results support the hypothesis that the molecular clock machinery in the chicken pineal gland is also sensitive to PACAP.