SUMMARY The intake of temperate forages by herbivores can be determined using the C 33 alkane naturally present in the forage and dosed C 32 alkane. To determine whether the technique can be used with tropical forages, the concentrations of C 33 alkane were determined in seven species. The leaves of Brachiaria decumbens, Digitaria decumbens, Pennisetum glaucum and Stylosanthes scabra contained sufficient C 33 alkane (> 50 mg/kg DM) for the estimation of dry matter intake. Low concentrations of C 33 alkane were found in the leaves of Setaria sphacelata, Sorghum sp. and Leucaena leucocephala. Setaria sphacelata was found to contain high concentrations of C 27 alkane and therefore intake could be estimated by using C 28 as the dosed alkane although the intake would possibly then be underestimated by c . 8%. Leaves of Sorghum sp. contained > 50 mg C 31 alkane/kg DM and, with C 32 as the dosed alkane, intake would possibly be underestimated by c . 5%. Leucaena leucocephala contained insufficient alkanes to estimate forage intake. The concentration of n-alkanes in Pennisetum glaucum and Sorghum sp. leaves decreased with age. It was concluded that some tropical forages contain insufficient C 33 alkane for the measurement of intake by the double alkane technique. In these species, a shorter chain length alkane can sometimes be used, but only with a reduction in accuracy in estimating intake.