14C-Distribution in the C3-chain of L-lactate after incubation of various 14-C-labelled prescursors ([1-14C] and [3-14C] glycerol; [3-14C] glyceraldehyde and glycerid acid; D- and L-[3-14C] serine; [1-14C] fructose and [6-14C] glucose) with homogenate showed that (1) most of the glycerol is metabolized to L-lactate via D-glyceraldehyde; the remainder may possibly form L-lactate via dihydroxyacetone; (2) a part of D-glyceraldehyde and D-glyceric acid may produce glycerol before L-lactate is formed; (3) D and L-serine do not form measurable amounts of L-lactate via D-glyceric acid; (4) rat-liver alcohol dehydrogenase (E.N.1.1.1.1) does not contribute to conversion to L-lactate of dihydroxyacetone phosphate from fructose nor of D-glyceraldehyde phosphate from glucose.