For tubular γ-ray applicators, a close approximation to a uniform dosage rate over a cylindrical surface of given length (l) and radius (h) may be obtained from an axially placed linear radioactive source of the same length, subdivided into three contiguous equal lengths, the outer sources having a higher linear density (ρ2) than that of the inner source (ρ1). The relation between ρ2 and the shape factor l/h has been determined on the basis of Sievert's expression for the γ-ray dosage rate near to an unscreened uniform linear source. Calculations of actual dosage rates are based on Sievert's formula for a linear source enclosed in an absorbing cylinder. The results, which have been confirmed experimentally, are presented in graphical form by two charts, which facilitate the planning of tubular applicators. One of these graphs gives the percentage content of the inner source, while the other gives the milligramme-hours required for a dose of 1000 r, for a comprehensive range of the shape factor.