The liver-enriched transcriptional activator protein DBP accumulates in hepatocytes of adult rats according to a strictly controlled circadian rhythm. DBP is not detectable in liver nuclei during the morning hours. Its level raises sharply during the afternoon and reaches a maximum at about 8 p.m. During the night the cellular DBP concentration decreases below detectability. This oscillation is "free running," transcriptionally regulated, and may be under the negative control of glucocorticoid hormones. In keeping with the rhythmicity of DBP accumulation, the albumin gene, a putative target of DBP, is transcribed more efficiently in the evening than in the morning.