The secreted alkaline phosphatase (SEAP) reporter system has been used to investigate the activity of known or putative promoter/enhancer elements [8] . As a reporter, SEAP has several important advantages over other reporters, such as high sensitivity and specificity both in vitro and in vivo [9] [10] [11] [12] . SEAP is a C-terminal truncated mutant of the membrane-anchored, placental alkaline phosphatase [13] . Removal of the anchoring domain results in secretion of the enzyme into the culture medium or blood stream, thus enabling repeated sampling from living cells or animals. Expression of the gene can be detected using chemiluminometry [14] . The secreted form of alkaline phosphatase is extremely heat stable, and its activity can be detected following the inactivation of endogenous alkaline phosphatases by heating. Therefore, it is easy to distinguish between exogenous and endogenous SEAP activity. SEAP assays can also be coupled to a luciferase reaction by incubation with the substrate, firefly D-luciferin-O-phosphate. The product of the first reaction, luciferin, then becomes a substrate for luciferase. This assay protocol improves the sensitivity of the reporter assay system, thus enabling its broader application [15] .