The expression of the spo0A-lacZ fusion gene was partially repressed in the presence of an excess of glucose. Expression was restored either by the mutation sigA47(crsA47) or by addition of decoyinine, an inhibitor of GMP synthetase, to the medium. By constructing a lacZ fusion with a smaller fragment of the spo)A gene, we observed a beta-galactosidase profile in which expression was completely repressed by an excess of glucose. This expression was restored by the addition of decoyinine. These results indicate that the expression of the spo0A gene is regulated by at least two different mechanisms, one sensitive to glucose, the other not. Furthermore, the glucose-sensitive regulation was shown to reside at the transcriptional level. It is likely that the reduced expression of the spo0A gene in the presence of glucose at an early stage of sporulation causes the repression of sporulation.