Previous studies have shown that during hypoxia there is increased expression of several genes such as immediate early genes. The present study tests the hypothesis that calcium and cAMP (cyclic adenosine 3',5'-monophosphate) will alter gene transcription during cerebral hypoxia in guinea pig fetus. Pregnant guinea pigs of 58 days gestation were exposed to either 21% O2 (normoxic) or 7% O2 (hypoxic). Tissue hypoxia in the fetus was confirmed biochemically by decreased levels of ATP and phosphocreatine. In vitro transcription assay was used to measure the gene transcription in the presence of different concentrations of calcium, cAMP, and both in cerebral nuclei isolated from 24 normoxic and 24 hypoxic fetal guinea pigs. The transcription assay was performed in a medium containing ATP, GTP, CTP, UTP and 3H-UTP. In hypoxic nuclei, gene transcription due to free RNA polymerase increased 83.63 pmoles/mg/hr (11.61%) as compared to that in normoxic nuclei. However, gene transcription due to chromatinbound RNA polymerase did not change. 8-bromoadenosine cyclic monophosphate (≤100 uM) did not change transcription in either normoxic or hypoxic conditions. Calcium chloride 250 nM increased gene transcription due to free RNA polymerase by 119.19±8.92 pmoles/mg/hr and 153.02± 9.05 pmoles/mg/hr in normoxic and hypoxic groups, respectively (p<0.05), but, there was no effect on gene transcription due to chromatin-bound RNA polymerase. In the presence of calcium (250 nM) and cAMP (10 uM), the transcription due to free RNA polymerase increased by 211.84±18.06 pmoles/mg/hr and 222±39.32 pmoles/mg/hr in normoxic and hypoxic groups, respectively, however, the gene transcription due to chromatin-bound RNA polymerase did not change. The results show that cAMP has a synergistic effect with calcium on free RNA polymerase-mediated transcription in normoxic nuclei but not in hypoxic nuclei. We conclude while during normoxia, calcium requires cAMP to integrate its signal transduction, during hypoxia increased intranuclear calcium alone may control gene transcription through Ca2+/calmodulin-dependent protein kinase (CaMK) and phosphodiesterase, or CaM-kinase kinase.