Two broiler experiments were conducted to assess the relative bioefficacy of liquid DL-Met hydroxy analog-free acid (MHA-FA) and DL-Met (DLM). Exponential regression analysis was used to determine biological efficacy based on body weight, feed conversion, and carcass responses to dietary Met source. In Trial 1, four graded inclusion levels of DLM and liquid MHA-FA (0.06, 0.12, 0.18, and 0.24%) were each added to a basal diet that met the nutrient and energy requirements of broiler chickens, with the exception of Met + Cys. In four additional treatments, diluted DLM (65%) was added at the same supplementation levels as pure DLM and liquid MHA-FA. In the 42-d trial, broilers responded significantly (P < 0.05) to the supplements. Regression analysis revealed that liquid MHA-FA was 68% (weight gain), 67% (feed conversion), 62% (carcass yield), and 64% (breast meat yield) as efficacious as pure DLM on an as-fed basis. Responses to liquid MHA-FA and diluted DLM were very similar at corresponding supplementation levels. Diluted DLM as an internal standard confirmed that exponential regression analysis was a statistically valid technique for determination of the relative efficacy of nutrient sources. In Trial 2, five graded inclusion levels of each DLM (0.040, 0.091, 0.152, 0.222, and 0.303%) and liquid MHA-FA (0.045, 0.102, 0.170, 0.250, and 0.350%) were added to a basal diet limiting in Met + Cys but adequate in all other nutrients and energy. Liquid MHA-FA was 72% (weight gain), 51% (feed conversion), 48% (carcass yield), and 60% (breast yield) as efficacious as DLM on a weight-for-weight basis.