SUMMARY:Forty mould species, 30 of which were from the generaAspergillus, Penicillium, FusariumandMucor, were examined for their ability to utilize the lactose in whey and to produce fat in the mycelium in stationary cultures.In terms of lactose consumed and weight of mycelial felt produced the most promising species wereA. ustus, P. frequentans, P. oxalicumandP. notatum.The first three of these warrant further study as fat producers.