IT has been known for some time that stars lose mass between their birth on the main sequence and their death as white dwarfs (or as neutron stars or black holes for more massive stars), and the existence of the solar wind shows that not all the mass loss occurs in a last gasp to form a planetary nebula. Mass loss has also been observed in O–B stars (see refs 1–3), and in red giants4, but the mass loss rates observed in these stages do not seem sufficient to explain all of the mass loss required for stars to become white dwarfs. The question has always been at what stages and in what manner this excess mass was lost. Suggestions have tended to favour helium flashes for stars with M < 2.25M⊙ and possibly double shell instability flashes for stars in the range 2.25M⊙ < M < 8M⊙. Although it is possible that a significant mass is lost during these stages, there is no quantitative support for this speculation, and in particular none for the helium flash. We show here that there is increasing evidence for substantial mass loss during the immediate post-main sequence stages when the star is moving from the main sequence to the giant branch on the Hertzsprung–Russell diagram.