The 13C magnetic resonance spectra of 19 complexes of acetylacetone have been recorded and are compared with their 1H spectra and the i.r. stretching frequencies of the ring atoms. The 13C shifts of the CH3 and ring CH groups for first- and second-row elements are explained largely in terms of first-order electric field shifts, the coefficients of proportionality between the 13C and 1H shifts being ca.–4·2 for CH3 and +0·94 for CH. The CO 13C shifts appear to be related to the CO and CC i.r. stretching frequencies. Serious deviations from these generalisations are observed for elements with filled or partly filled d-orbitals.