Addition of whey protein hydrolysate (WPH) to whey permeate fermentations, by Lactobacillus helveticus. to produce lactic acid was investigated. Three to four percent (w/w) supplementation with WPH solution (10% w/w protein) was required to obtain high lactose conversion and lactic acid yield in a fermentation time of 30-40 h. At this percentage supplementation, the nitrogen content of the media was 0.06-0.09% w/w. The bacteria used around 0.02% w/w nitrogen during fermentation. thus there was an abundance of unused nitrogen remaining at the end of fermentation. At 3-4% supplementation, it was calculated that around 36-47% of whey protein concentrate produced from whey would be required to supplement the whey permeate fermentation in the form of the hydrolysate.