This study examined the effect of bovine colostrum (BC) supplementation on the tissue composition of resistance trained (T) and untrained (UT) limbs. Using a double-blind design, subjects were randomly allocated to 60 g day(-1) of BC ( n=17) or whey protein (WP) ( n=17) during 8 weeks of resistance training of the elbow flexors (EF) of their non-dominant arm (T). Axial magnetic resonance images of both upper arms, maximal voluntary isometric torque (MVC) of EF, and the one repetition maximum (1RM) for bicep curls were measured pre- and post-supplementation. There were no differences in macronutrient intakes ( P>0.28) or the volume of training completed by T ( P=0.98) between the two groups. T of BC experienced a significantly greater increase in circumference [BC 2.3 (3.0)%, WP 0.0 (4.2)%; P=0.05] and cross-sectional area (CSA) [BC 4.2 (6.0)%, WP -0.2 (8.3)%; P=0.05] compared with WP, due principally to a greater increase in skin and subcutaneous fat (SSF) CSA [BC 5.5 (10.9)%, WP -2.7 (14.1)%; P=0.03]. No tissue compartment changed significantly in UT of either group ( P>0.05). MVC and 1RM increased for T and UT in both groups ( P<0.05), but the increases were not different between groups ( P>0.32). Since the SSF compartment increased in T but not UT, and fat turnover in adipocytes is under hormonal control and would not be localised to one arm, we suggest that the increase in SSF CSA in T of BC may have been due to an increase in skin CSA, rather than fat.