The circular dichroism (CD) method has been used for studying the stereochemistry of steroid alkaloids containing an azomethine ring - petiline and petisine. In the CD spectrum of petiline a Cotton effect (CE) is observed in the 235 nm region which is due to a n → π* transition in the azomethine chromophore. The negative sign of this CE shows the 25S configuration in petiline. An analysis of CD spectra has shown that the 25S configuration is retained when petiline is oxidized to petisine. © 1986 Plenum Publishing Corporation.