High concentrations of 422 g sophorolipids l−1 were produced using a two-stage cultivation process: first deproteinized whey concentrate (DWC) containing 110 g lactose l−1 was used for cultivation of the yeast Cryptococcus curvatus ATCC 20509, resulting in 34 g dry weight l−1, 20 g single-cell oil l−1 and reducing the chemical oxygen demand (COD) from 159 g l−1 to 35 g oxygen l−1. Afterwards cells were disrupted by passing the cell suspension directly through a high pressure laboratory homogeniser. After autoclavation, the resulting crude cell extract containing the single-cell oil served as substrate for growth of Candida bombicola ATCC 22214 and for sophorolipid production in a second stage. When the single-cell oil was consumed, repeated feeding of 400 g rapeseed oil l−1 was started increasing the yield of sophorolipids to 422 g l−1. A simple technique for product isolation, sedimentation, could be used to harvest the crude sophorolipids. © Rapid Science Ltd. 1998