Twelve sun¯ower (Helianthus annuus L) cultivars grown in Spain were analysed and tested in experiments with rats. The dehulled seeds contained an average of 32.2 MJ kg À1 dry matter (DM) gross energy, 653 g kg À1 DM fat, 60 g kg À1 DM total non-starch polysaccharides (NSP) and 6 g kg À1 DM Klason lignin. The sun¯ower seed hulls contained 20.2 MJ kg À1 DM gross energy, 53 g kg À1 DM fat, 562 g kg À1 DM total NSPs and 239 g kg À1 DM Klason lignin. The sun¯ower samples were dehulled and partially defatted (to $17% fat) and included in diets for rats. The dehulled, partially defatted samples contained on average 74.6 g nitrogen kg À1 DM and 1.409 mg g À1 phenolic compounds (chlorogenic acid caffeic acid derivative 1 derivative 2) varying from 0.677 to 2.847 mg g À1 . Groups of ®ve growing rats were fed diets (9.38% crude protein) containing one of the sun¯ower cultivars as the only source of protein. Apparent ileal and faecal digestibilities were determined by using an indigestible marker (Cr 2 O 3 ) and faecal digestibility based on total faecal collections. Apparent ileal, caecal and faecal digestibilities of organic matter were 81.2±91.5% (P = 0.05), 95.8±97.1% (P = 0.005) and 94.7± 95.3% (P = 0.94) respectively. The apparent faecal digestibilities of DM, energy and protein (N Â 6.25) were 93.2±93.8%, 93.5±94.3% and 81.6±84.3% respectively with no differences among cultivars. Biological value (BV) ranged between 63.8 and 73.2% (P = 0.0001) and net protein utilisation (NPU) between 59.9 and 69.5% (P = 0.0001). BV and NPU were positively correlated with lysine and threonine contents, but no correlation with the analysed phenolic compounds was detected.