Dissolution of 17α-hydroxyprogesterone (1) in 80% sulfuric acid gave two D-homosteroids through C (13)-C (17) bond migration, 17aβ-hydroxy-17aα-methyl-D-homoandrost-4-ene-3, 17-dione (2) and 17a-methylene-D-homoandrost-4-ene-3, 17-dione (3), in 53 and 9% yields, respectively. The latter product was also obtained in 73% yield from the reaction of 1 with 90% sulfuric acid. Proton nuclear magnetic resonance (¹H-NMR) studies of the acid solutions revealed that the D-homoannulation of 1 to 2 occurs rapidly even in 80 or 90% sulfuric acid, and that 2 is dehydrated rapidly to 3 in 90% sulfuric acid. The D-homoannulation was demonstrated to be an initial step in the color and fluorescence reaction of 1 with sulfuric acid.