The objective of this study was to evaluate the effect of rumen-protected lysine and methionine supplementation during the transition period on lactation performance by dairy cows. A meta-analysis was conducted with a data set comprised of 20 unpublished feeding trials; trials were designed as continuous lactation trials and evaluated the effects of lysine or lysine/methionine supplementation in dairy cows. For all comparisons, data were analyzed using Proc Mixed of SAS with treatments as fixed effects and trial as a random effect with treatments weighted according to the number of experimental units reported in each trial. Our first comparison evaluated the effects rumen-protected lysine and/or methionine supplementation in pre- and postpartum (PREPOS), or only postpartum (POS) compared with cows fed a basal diet (CON). Cows supplemented with rumen-protected amino acid PREPOS produced 0.9 and 1.0 kg/d more (P < 0.01) milk and ECM, respectively, than cows supplemented POS or CON. Milk fat yield was greater for cows supplemented PREPOS compared with CON (P < 0.01; 1.59 vs. 1.55 kg/d). Milk protein yield was greater for cows supplemented PREPOS and POS compared with CON (P < 0.01; 1.21 vs. 1.18 kg/d). Our second comparison evaluated the effects of supplementation pre- and postpartum of rumen-protected lysine and methionine (RPLM), or rumen-protected lysine in combination with methionine from dietary ingredients (RPLDM) compared with cows fed a basal diet (CONT). Cows supplemented RPLM produced 1.6 and 2.2 kg/d more (P < 0.01) milk and ECM than cows supplemented with RPLDM or CONT. Milk fat yield was greater for cows supplemented RPLM compared with RPLDM and CON (P < 0.01; 1.60 vs. 1.51 kg/d). Milk protein yield was greatest for cows supplemented with RPLM, intermediate for RPLDM, and lowest for CONT (P < 0.01; 1.22, 1.18, and 1.15 kg/d, respectively). These results indicate that supplementation with rumen-protected lysine and methionine throughout the entire transition period enhances lactation performance by dairy cows.