We have studied steroid sulfate conjugates in serum samples from 17 children with Prader-Willi syndrome (PWS) by extraction, enzymatic hydrolysis and chromatography of the hydrolysed, free steroids. The chromatograms in patients with PWS can be divided into 2 classes. Ten (4 with the deletion on chromosome 15 and 6 without) of 17 had a normal pattern with dehydroepiandrosterone (DHEA) as the only steroid detected. However, 7 out of 17 (3 with the deletion and 4 without) had a very different pattern. The chromatogram derived from these hydrolysates had 5 major peaks. One of these was DHEA; a second peak was tentatively identified as 16 alpha-hydroxy-DHEA on the basis of column retention time and immunoreactivity. The remaining 3, more polar, compounds have not yet been identified. The presence of unusual steroid sulfoconjugates in serum may correlate with other features of PWS and may be the basis for dividing PWS into two separate disease states: a) PWS-1 associated with DHEA-S as the only sulfo-conjugate and b) PWS-2 associated with unusual sulfo-conjugates. One interesting possibility is that these sulfo-conjugates may have a hormonal function, even though no function has yet been recognized for DHEA-S. Then, PWS may be the common clinical manifestation of a variety of different defects in the sulfo-conjugate metabolic pathway.