INTRODUCTION There were numerous reports on the influence of the surgical caponization of chickens in the areas of growth performance (Wang, 2001; Lin and Hsu, 2002), taste panel scores (Kuo, 2002), organ and carcass part ratios (Lin and Hsu, 2003b), muscle compositions (Kuo, 2002), muscle physical properties (Lin and Hsu, 2002), skin and muscle color values (Kuo, 2002; Lin and Hsu, 2003b), bone traits (Lin and Hsu, 2003a) and behavior (Wang, 2001). Lin and Hsu (2003a) have been published on the influence of surgical caponization on the plasma testosterone concentration, which intact birds was higher (p0.05) than that of capons. A study by Kazeniac (1961) indicated that inosine monophosphate (IMP) produced a major contribution to mouth satisfaction and had the effect of intensifying the flavor effects of other compounds. This study also showed that inosine (HxR) and hypoxanthine (Hx) were bitter. It had been suggested that IMP and its degradation products were important components of the flavor-precursor complex in chicken muscle (Dannert and Pearson, 1967). Terasaki et al. (1965) found that the greater the IMP content in the muscle of chickens, the better they tasted. Davidek and Khan (1976) introduced the term "K values" as an indicator of the freshness of fish meat and chicken muscle. Little information was available on the influence and role of male sex hormones on fluctuations in ATP-related compounds. This study, therefore, investigated the influence of testicular activity on the muscle composition, ATP-related compounds, the shear value and the taste panel scores on Taiwan country chicken cockerels at 28 weeks of age.