Heat transfer and pressure drop characteristics for the flow across banks consisting of plain (unfinned) helical tubes in a multistart arrangement with essentially uniform inclination angles, uniform longitudinal pitches and hence essentially equal heat loads per tube, but with tube pattern changing continuously around the perimeter, have been reduced analytically to the relatively well-known heat transfer coefficients and friction factors for the flow across banks of straight tubes with in-line and regularly staggered tube patterns. For this purpose, correction factors for the effects of tube inclination and of the number of tube rows are introduced. The effective average values of the free flow area—which determine the effective velocity and hence the effective Reynolds number—and the effective arrangement factors are obtained by integration of the local values. The apparent differences of the heat transfer and pressure drop correlations obtained by the two experimental investigations known—the Waagner-Biro experiments on the prototype tube bundle of the steam generators for the OECD High Temperature Reactor Project Dragon and the data of Glaser on regenerator inserts—have been explained quantitatively by the different approach employed for calculating the free flow area. Using the expressions for the effective average free flow area and the correction factors for tube inclination and tube row numbers, agreement of the heat transfer and pressure drop data of both experimental investigations with each other and, what is more, with straight-tube data is achieved. The suggested heat transfer and pressure drop correlations for banks of helical tubes are valid for gases and liquids with Prandtl numbers above 0.1. This range includes applications to steam generators of gas-cooled and liquid-cooled reactors (and cryogenic applications as well). For heat exchangers and steam generators of liquid-metal-cooled reactors—that is for Prandtl numbers of the order of 0.01—a different heat transfer correlation is developed, which is based on available data obtained with liquid metal flowing across banks of straight tubes.