This trial aimed to evaluate the bioavailability of DL-2-hydroxy-4-(methyl) butanoic acid (DL-HMBA) and a poly-herbal ingredient (PHI) in relation to DL-methionine (DLM) on broilers. A sample of 1100 broiler chickens of the Cobb 500 strain, both male and female, were fed either a basal diet without industrial methionine supplementation or a basal diet that was supplemented with three DL-HMBA levels (0.170, 0.340, and 0.511%) or three DLM levels (0.111, 0.221, and 0.332%) in an amount equivalent to 65% of the respective DL-HMBA levels (on a product weight basis) and three levels of PHI (0.111, 0.221, and 0.332%) in amounts equivalent to the used DLM levels from 1 to 21 days of age. The simultaneous linear regression analysis (slope ratio) revealed a relative bioavailability of DL-HMBA of 39% compared to that of DLM for weight gain and 44% for feed conversion. However, the performance data from birds that were supplemented with PHI did not significantly adjust to simultaneous regression designs; therefore, it was not possible to determine the PHI bioavailability in relation to the DLM. Considering together all of the studied parameters, the relative bioavailability of DL-HMBA was 42% compared to the DLM on a product basis.