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Abstract. Freeze-etch electron microscopy was applied to milk fat globules to observe surface details. A remarkable array of filaments, approximately 0.5 micro m in length, was seen on human, but not bovine, globules. Heating human globules removed the filaments that were identified as high molecular weight glycoproteins by freeze-etch and gel electrophoretic analysis of the heating medium. Extraction of these globule glycoproteins was slight at 60 Celsius for one minute but substantial and tending to plateau at 80 Celsius for one minute. Such heat-induced alterations of the milk fat globule surface provide an alternative or additional explanation to milk lipase inactivation as the cause of reduced milk fat absorption from heated milk by the preterm infant. [ABSTRACT FROM AUTHOR]