Abstract A strong correlation existed between degree of cold-induced lipolysis and amount of lipoprotein lipase activity associated with the cream fraction of milk. This correlation was true in milk samples taken at different stages of lactation and in samples of morning and afternoon milk. The cold-induced binding of lipase to cream occurred slowly but reached a maximum during 3 to 5h of cold storage. Cooling of sensitive milk samples to 17°C caused significant amounts of lipase to bind to cream, but the effect was maximal at or below 12°C. Heparin detaches lipoprotein lipase from casein micelles, and therefore, increased the amount of free lipoprotein lipase in milk serum. This had little effect on the amount of lipase that bound to cream at room temperature but significantly increased both the amount of lipase bound and lipolysis if the milk was cooled. Addition of heparin to already cooled milk had less effect on both binding and lipolysis. Availability of free lipase in milk serum in combination with physical events during cooling of milk favors binding of lipoprotein lipase to milk fat globules. This leads to increased lipolysis.