Free-gossypol content of the seed of South African cotton cultivars cultivated in different regions. Representative seed samples of the 10 most important cotton cultivars, each cultivated in the 10 most important production localities in the Republic of South Africa, were collected during the harvesting season of 1986 and analysed in duplicate for free-gossypol content. The free gossypol was extracted with an aqueous acetone solution and determined spectrophotometrically at a wavelength of 440 mu. Because highly significant cultivar X locality interactions were found, one-way analyses of variance were carried out to test separately for differences between cultivars and localities. Although the average free-gossypol content differed highly significantly (P <0,01) between cultivars and between localities, the most important result was probably the high average free-gossypol content of all 10 cultivars on all 10 production localities, viz. 0,64% (OM), which is higher than the average free gossypol in whole cottonseed reported in the literature. The high free-gossypol content of the seed of tested South African cotton cultivars should be taken into account where cottonseed is included in diets for ruminants, especially dairy cows.