This study examined the feasibility of using the promoter of the pig parotid secretory protein (PSP) gene for expression of the phytase transgene in mouse models. The pig parotid secretory protein gene is specifically expressed at high levels in the salivary glands. The 10-kb upstream promoter region of the gene necessary for tissue-specific expression has been identified. We have constructed phytase transgenes composed of the appA phytase gene from Escherichia coli driven by the upstream promoter region of the pig PSP gene with a 3' tail of either bovine growth hormone or the pig PSP gene polyadenylation signal. Transgenic mouse models with the construct showed that the upstream region of the pig PSP gene is sufficient for directing the expression of phytase transgenes in the saliva. Expression of salivary phytase reduced fecal phytate by 8.5 and 12.5% in 2 transgenic mouse lines, respectively. These results suggest that the expression of phytase in salivary glands of monogastric animals offers a promising biological approach to relieve the requirement for dietary phosphate supplements and to reduce phosphorus pollution from animal agriculture.