The aim of the present study was to verify whether or not plasma growth hormone (GH) concentrations are correlated with temperament in mithuns (Bos frontalis), a semiwild ruminant. Therefore, a total of 69 female mithuns from four different strains, viz., Arunachal, Nagaland, Mizoram, and Manipur, were divided into six age groups (Group I, 0-6 months; Group II, >6-12 months; Group III, >1-2 years; Group IV, >2-2.5 years; Group V, >2.5-3.0 years; Group VI, >3.0 years). Blood samples were collected weekly for 6 consecutive weeks and assayed for plasma GH. Temperament was scored on a 6-point scale, 6 were being very aggressive and 1 docile. Body weights of all animals were recorded once a week for 6 consecutive weeks GH concentrations and temperament scores were found to differ significantly between groups. Strain had significant effects on blood GH levels and temperament. Blood GH concentrations and temperament of Manipur mithuns were significantly higher than those of the other three strains within each group, for all groups. Across groups III to VI, blood GH levels and temperament among Nagaland, Mizoram, and Arunachal mithuns did not differ. Overall, the strain with the highest blood GH concentrations also had highest temperament scores. The Manipur strain had the highest blood GH levels and exhibited the most aggression (r = 0.95), and Arunachal mithuns, the lowest (r = 0.93). Temperament scores tended to decrease with increasing age for all four strains. Coefficients of correlation between blood GH and temperament among strains within each group, for all groups, were found to be significant. The highly positive correlation (r = 0.94) between blood GH concentrations and temperament for all animals, regardless of age and strain differences, clearly indicates the relationship between blood GH and temperament in mithuns. In conclusion, our results suggest that peripheral blood GH levels can influence temperament in mithuns.