The structures of the title compounds were solved by direct methods and refined by anisotropic full-matrix least-squares methods. 4,11-Pregnadiene-3,20-dione, C21H28O2(1) crystallizes in the monoclinic space groupP21 (Z=2). The unit cell parametersa, b, c (A), and β (°) were: 12.319(2), 7.700(2), 9.717(2), 109.41(2). TheA- andC-rings exhibit intermediate sofa-halfchair conformations. TheB-ring has a chair conformation and theD-ring assumes an intermediate envelope-half-chair conformation. The progesterone side chain has a typical conformation; the C16−C17−C20−O20 torsion angle is −15.1(4)°. 21-Methyl-20-oxa-4-pregnene-3,20-dione, C21H30O3 (2) crystallizes in the orthorhombic space groupP212121 (Z=4). The unit cell parametersa, b, c (A) were: 12.926(2), 19.447(4), 7.313(1). The progesterone side chain has an unusual conformation; the C16−C17−C20−O20 torsion angle is 174.6(4)°. TheA-ring has a 1α, 2β-half-chair conformation, ringsB andC exhibit chair conformations and ringD is in a 13β,14α-half-chair conformation.