Immature female turkeys (7 wk old) were treated with 5-azacytidine, a cytidine analog that has been shown to inhibit cytosine methylation in eukaryotic DNA. Such methylation has been repeatedly implicated in the control of specific gene expression in higher vertebrates. Turkeys administered 5-azacytidine (5 mg/kg) by intravenous injection daily for 5 days exhibited elevated (P less than .05) circulating prolactin (Prl) levels, whereas hens treated with saline, cytidine, or 6-azathymine did not show altered circulating Prl levels. Absence of response upon treatment with the normal nucleoside cytidine or the 6-aza analog of thymine reasonably eliminates nonspecific drug-induced stress as the cause of Prl level elevation. Based on these findings, DNA methylation is implicated in the control of circulating Prl levels in the young turkey.