Forced-convection heat transfer to supercritical helium has been investigated. The test section is a 1. 25 left bracket mm right bracket inner diameter and 200 left bracket mm right bracket long straight tube through which helium flows upward or downward, heated uniformly. The conditions covered are inlet fluid temperature between 4. 7 and 10. 8 left bracket K right bracket , system pressures of 0. 3, 0. 5 and 0. 8 left bracket MPa right bracket , mass velocities of 20, 40 and 80 left bracket kg/(m**2 multiplied by (times) S) right bracket and heat fluxes of 500, 1000, 2000 and 4000 left bracket W/m**2 right bracket . Experimental results on the distributions of wall temperature and heat transfer coefficient are presented and a comparison of experimental results between those for upward and downward flow directions and discussion about the differences between them are done in the light of the effect of buoyancy.