Abstract Conformational analysis of some tetra-and octahydro-11H-pyrido [2, 1-b] quinazolin- 11-ones 1-3 by 1 H and 13 C nmr revealed that the 9-methyl-6, 7, 8, 9-tetrahydro derivative exists mainly in the conformation containing the methyl group in a quasi-axial orientation. Of the 1, 2, 3, 4, 5, 6, 7, 8-octahydro compounds, the 9-methyl derivative 3e contains the methyl group in a quasi-axial position, while that in the 7-methyl and the 8-methyl derivatives 3c, ...