In the present article an attempt is made to summarize the steric requirements and the influence of neighboring groups which determine the course of intramolecular radical reactions. Steroids are used as substrates for these reactions, since here the spatial arrangement of the ring members and the distances between substituents are largely fixed. Furthermore, intraniolecular free-radical reactions are of practical importance in steroid chemistry in connection with substitution at non-activated carbon atoms. Almost all the reactions discussed begin with the formation of an oxygen radical by oxidation of an alcohol with lead tetraacetate or by homolysis of the corresponding hypoiodite. k . -A . Ogg and M. Polanyi, Trans. Faraday SOC. 31, 482 (1935), R. A . Herrnrann and R. M. Noyes, J. Amer. chem. SOC. 78, 5764 molecular processes. The relative positions of reaction centers are very easily assigned in the Of fused-ring cyclohexane derivaibid. 83, 1547 (1961), are 'substitutions of this type. [2a] J.