OBJECTIVE: To investigate the gene expression of Kiss-1 in the hypothalamus of true precocious female rats at various stages of development. METHODS: Forty 5-day-old normal female Sprague-Dawley rats were randomly assigned into four groups of 10 rats: Control group 1, Control group 2, Model group 1 and Model group 2. The rats from the two model groups were injected with 300 μg of danazol at 5 days of age to induce true precocious puberty. The two control groups were injected with normal saline instead. For the determination of Kiss-1 mRNA expression in the hypothalamus, the rats of the Model group 1 were sacrificed during the first diestrus (early puberty) and meanwhile the rats of the Control group 1 were sacrificed when they were at prepuberty; the Control group 2 rats were sacrificed at the first diestrus (early puberty); the rats of the Model group 2 were sacrificed during the second diestrus (middle puberty). The expression of Kiss-1 mRNA in the hypothalamus in the four groups was detected using semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). RESULTS: Kiss-1 mRNA expression in the hypothalamus in Model group 1 and Model group 2 increased by 1.4-fold and 2.8-fold, respectively, compared with that of Control group 1 (P<0.05). Model group 2 showed significantly higher Kiss-1 mRNA levels than Model group 1 (P<0.05). There were no statistical differences in the Kiss-1 mRNA expression between Control group 2 and Model group 1. CONCLUSIONS: Gene expression of Kiss-1 is associated with the developmental period of true precicous puberty, suggesting that Kiss-1 might play a role in the pathogenesis of this disorder.［Chin J Contemp Pediatr, 2006, 9(1):59-62］