A metallic heat exchanger tube has fins which run helically around the outside of the tube, are molded integrally therefrom and are of continuous design and the fin base of which protrudes substantially radially from the tube wall, and with primary grooves located between respectively adjacent fins. At least one undercut secondary groove is arranged in the region of the groove base of the primary grooves. The secondary groove is delimited toward the primary groove by a pair of mutually opposite material projections formed from the material of respectively adjacent fin bases and the cross-section thereof is varied at regular intervals without having an influence on the shape of the fins. There is a spacing between the opposite material projections, the spacing being varied at regular intervals, as a result of which local cavities are formed.