Lactarius volemus is a species of fungus in the genus Lactarius. It is distributed in warm temperate regions and northern areas of the Northern Hemisphere, and has been collected in Europe, North America, Central America, and Asia. A mycorrhizal fungus, its fruit bodies grow on the ground at the base of various species of trees from summer to autumn, either individually or in groups. It is considered a choice edible mushroom, and is sold in markets in Asia. There are several other Lactarius mushrooms that resemble L. volemus, such as the closely related edible species L. corrugis, but they can be distinguished by differences in distribution, visible morphology, or microscopic characteristics. L. volemus produces a white spore print and has roughly spherical spores about 7–8 micrometres in diameter.
The colour of the L. volemus mushroom varies from apricot to tawny, and the cap may be up to 11 cm (4.3 in) wide. The pale golden yellow gills on the underside of the cap are closely spaced and sometimes forked. One of the mushroom's most distinctive features is the large amount of latex ("milk") that it exudes when the gills are damaged, leading to the common names weeping milk cap and voluminous-latex milky. It also has a distinctive fishy smell, which does not affect the taste. The fruit bodies have been chemically analysed and found to contain several sterols related to ergosterol, some of which are unique to this species. The mushroom also contains a natural rubber that has been chemically characterized. Phylogenetic analysis suggests that Lactarius volemus represents several species or subspecies, rather than a single taxon.