Supplementation of rumen-protected AA is often used to compensate blood deficiency of Met, Lys and His for optimal milk protein synthesis in dairy cows. The bioavailability of RP-Met and -Lys has been measured using the plasma free AA dose-response technique. However, the characteristic endogenous His pool may increase uncertainty to apply the technique on RP-His. Therefore, our objective was to determine the linearity in plasma His by infusing His abomasally. Five multiparous lactating Holstein cows (149 ± 92 DIM) fitted with ruminal cannulas were used in a 5 × 5 Latin squares with 7-d experimental periods. All cows were fed a basal diet to provide adequate energy and metabolizable protein (NRC, 2001). Treatments were 0, 6, 12, 18, and 24 g/d of abomasally infused His. Blood samples were collected at 2, 4, 6, and 8 h after the morning feeding on the last 3 d of each period and composited by day. Milk samples were also collected on the last 3 d of each period. Milk production and components data, and plasma metabolites were analyzed with the PROC MIXED procedure of SAS. Relationships between plasma His and His infused were described by the PROC REG procedure of SAS. Intake of DM was not affected by His infused. Milk lactose concentration increased quadratically to the His infusion. Milk yield and other milk components (fat and true protein) were not affected by treatment. Plasma His concentration increased linearly with increasing amounts of His infused from 54.7 µM at 0 g/d to 70.2 µM at 24 g/d. Treatments had no effect on all other plasma AA, carnosine, and hemoglobin. Both plasma His concentration (µM) and the proportion of His in total AA were highly related to the amounts of His infused (r² = 0.93 and 0.97, respectively). We conclude that there is linear response of plasma His to His supplementation in this short-term study.