A method was developed t o i d e n t i f y r a d i o l a b e l e d DES and DES m e t a b o l i t e s i n b i o l o g i c a l f l u i d s and tissues. A f t e r a r a p i d i n i t i a l clean-up step, t h e b i o l o g i c a l samples were analyzed w i t h a single-column, reversed-phase, highpressure 1 i q u i d chromatography system. The parent compound and m e t a b o l i t e s were simultaneously resolved and t e n t a t i v e l y i d e n t i f i e d by comparing t h e i r r e t e n t i o n times t o those o f known standards. P o s i t i v e i d e n t i f i c a t i o n o f some m e t a b o l i t e s was achieved by f i e l d -d e s o r p t i o n and c a p i l lary-column massspectrometric analysis. and sample recovery was >80%. The method was found t o be r a p i d and r e p r o d u c i b l e ,