A helium transfer line adapted to be constructed in extended lengths and to carry liquid helium and/or 4.2.degree.K helium gas with minimum loss of refrigeration capacity due to heat leaks into and through the line. The transfer line, in its basic structure, comprises a fluid helium process line, radiation shielding, vacuum jacketing and a cryogenic coolant line in thermal contact with the radiation shielding and carrying a cryogenic coolant such as liquid nitrogen. Line components, comprising heat-stationed bayonets with or without LN.sub.2 bypass lines, expansion/contraction joints, and flexible sections and, if desired, valves, ell-sections and tee-sections, are designed to be integrated into the basic structure so that this structure may be carried through essentially the entire length of the line. Various combinations of these components in the transfer line make it possible to adapt the transfer line to a wide range of requirements dictated by such factors as space, and the relative positions of the two or more points of connection, i.e., a source of liquid helium and a refrigeration load to be cooled by the liquid helium.