Our objectives were to evaluate the effects of lecithin feeding on milk production and circulating markers of metabolic health in dairy cows fed palmitic acid (PA). In a split-plot Latin square design, 16 Holstein cows (160 ± 7 DIM) were randomly allocated to a main plot receiving a corn silage and alfalfa haylage-based diet with palm fat containing either moderate or high PA content at 1.75% of ration DM (MPA and HPA, respectively; BergaFat F-100 or F-100 HP containing 87 or 98% PA, respectively; Berg + Schmidt, Hamburg, Germany; n = 8/group). On each palm fat diet, deoiled lecithin was top-dressed at 0, 0.12, 0.24, or 0.36% of ration DM in a replicated 4 × 4 Latin Square design. Following a 14 d covariate period, lecithin treatment spanned 14 d with milk and blood collected during the final 3 d. Milk composition and pooled serum markers were measured. The statistical model included the fixed effects of PA type, lecithin level, period, and their interactions as well as the random effect of cow. Lecithin linearly decreased DMI (29.2, 28.7, 27.0 and 27.3 kg/d, P = 0.01). In cows fed HPA, lecithin feeding reduced milk fat content (interaction, P < 0.01) and tended to decrease milk fat yield (interaction, P = 0.10). Although no changes in milk yield were observed, a quadratic reduction in 3.5% FCM was observed with increasing lecithin feeding (P = 0.001). Lecithin linearly increased efficiency to produce ECM in cows fed MPA (P < 0.05). The proportion of 16C fatty acids (FA) in milk fat decreased linearly with lecithin level, whereas 18C FA increased linearly (e.g., 18:0; P < 0.01). De novo FA (<16C) tended to be reduced by lecithin (P = 0.08). Lecithin feeding increased MUN, relative to unsupplemented cows (0 vs rest, P = 0.01) and linearly increased serum FA concentrations (P = 0.01). Although increasing lecithin did not modify liver enzyme levels, several interactions were observed between palm fat type and lecithin level but were not of clinical importance. We conclude that lecithin feeding decreased DMI, increased MUN, and lowered milk fat content; therefore, rumen biohydrogenation was likely modified.