17beta-Oxazolinyl steroids 7a-g and 8a-g were synthesized. The Lewis acid-catalysed reactions of (20R)-3beta-acetoxy-21-azidomethyl-20-hydroxypregn-5-ene with substituted aromatic aldehydes led to the formation of 3beta-acetoxyandrost-5-enes substituted in position 17beta with oxazolinyl residues (7a-g). Oppenauer oxidation of the 3beta-hydroxy-exo-heterocyclic steroids yielded the corresponding Delta(4)-3-ketosteroids. The inhibitory effects (IC(50)) of both 3-hydroxy compounds 7a-g and their Delta(4)-3-keto counterparts 8a-g on rat testicular C(17,20)-lyase were investigated with an in vitro radioligand incubation technique. The 3-chlorophenyl- (8d), and the 4-bromophenyl-17beta-(2-oxazolin-5-yl)androst-4-en-3-one derivatives (8f) were found to be modest inhibitors (IC(50)=4.8 and 5.0 microM, respectively).