This method is applicable for determining activity of acid phosphatase (ACP), a heat-labile enzyme, in cooked, boneless, nonbreaded broiler marinated (83.65% meat) and nonmarinated (100% meat) breast and thigh and in a 50:50 blend of breast and thigh meat. The assay uses a self-indicating substrate that, when acted upon by ACP, loses a phosphate radical and becomes a highly fluorescent compound. Cooked meat is added to deionized distilled water in a 1:3 ratio, blended with a hand-held homogenizer, and then centrifuged at 2500 relative centrifugal force for 5 min. ACP activity in the filtrate is measured after shaking on a Vortex mixer 75 microL of the extract with a pH 5.00 acetate buffer containing a nonfluorescent aromatic monophosphoric ester substrate. The rate of fluorophore formation is monitored during a 3 min incubation period (38 degrees C) in a fluorometer, and ACP enzyme activity (mU/kg sample) is calculated. Three laboratories analyzed 6 cooked poultry products (marinated and nonmarinated breast, thigh, and 50:50 breast/thigh blend). Five cooking temperatures were used to generate different ACP activity levels, which were replicated twice with duplicate samples and duplicate sample tests representing 720 data points. Log10 ACP activity (mU/kg sample) performance repeatability and reproducibility standard deviations (sr and sR) and relative standard deviations (RSDr and RSDR) over 5 cooking treatments for 6 products were as follows: marinated breast: sr = 0.02, sR = 0.08, RSDr = 0.60%, RSDR = 2.12%; nonmarinated breast: sr = 0.02, sR = 0.04, RSDr = 0.66%, RSDR = 1.29%; marinated thigh: sr = 0.01, = 0.01, RSDr = 0.37%, RSDR = 0.37%; nonmarinated thigh: sr = 0.02, sR = 0.05, RSDr = 0.53%, RSDR = 1.43%; marinated 50:50 breast/thigh blend: sr = 0.01, sR = 0.05, RSDr = 0.36%, RSDR = 1.31%; nonmarinated 50:50 breast/thigh blend: sr = 0.01, sR = 0.04, RSDr = 0.32%, RSDR = 1.12%.