Sumnzary. The carefully controlled UV. irradiation of 3-hydroxyimino-d4-and 3-hydroxyimino-A4,A6-steroids yield as a result of vinyl and alkyl migration, lactams besides products expected.Rearrangement of conjugated steroidal ketonic nitrones yields N-substituted lactams as a result of vinyl migration (1 -+ 2) [Z]. Synthesis of the analogous N-nonsubstituted compounds 3 seems not to be feasible: The Beckmann rearrangement of the appropiate oximes gives only the alkyl migration isomers (e.g. 5 and 6 + 7) [3], and by irradiation 5 and 6 or similar unsaturated oximes show either a remarkable lack of reactivity [4], or syn-anti isomerization and fragmentation to ketone, followed by a slow and extensive decomposition [4] [5]. In no case have the least mentioned authors reported the formation of lactams as a result of a photo-Beckmann rearrangement. Nevertheless, from our previous work, a) the isolation of a lactam after UV. irradiation of 3-hydroxyimino-17~-acetoxy-androsta-l, 5-diene [6], and b) the photolability of conjugated lactams to give mainly dimers [7], suggest that the photoBeckmann rearrangement of 5 or 6 and of analogous oximes may take place, the primarily formed lactamic products not being detected owing to their further photochemical reaction.A systematic study was therefore undertaken and the following were found to be the most suitable conditions for photo-rearrangement : 1) Use of a medium pressure Hg lamp without filter, short irradiation time (-30 min), and low concentration (-O.lyo) ensure that the photo-Beckmann rearrangement takes place quickly, and secondary reactions (dimerization) are minimized; 2) use of a hydroxylic solvent, l)For part V, see [l].