In this work, the detailed NMR studies and full C-13 NMR assignments for five diterpenoids isolated from Sideritis caesarea and Sideritis athoa are described. The assignments are based on a combination of 1D and 2D NMR techniques including H-1, C-13, H-1-H-1 COSY, gHSQC [(1)J(C,H)] and gHMBC delta(C) [(n)J(C,H) (n = 2 and 3)] and NOESY experiments. Copyright (C) 2011 John Wiley & Sons, Ltd.