Four diterpenes, taxodone, taxodione, 11-​hydroxymontbretol, and ferruginol, were isolated from Taxodium distichum (L.) Rich seeds.  Taxodone and taxodione were isolated before from the same source and have been reported to possess antitumor activity.  11-​Hydroxymontbretol and ferruginol were isolated for the first time here from the genus Taxodium.  The structures of the isolated compds. was detd. through intensive spectral anal.  HIV-​1 PR inhibitory activity for the four compds. showed that only taxodione had a potent effect in 0.1 mM concn.