The surface acid-base characteristics of samples of cellulose, pine wood, and kenaf powder were determined by inverse gas chromatography (IGC). The test substrates were packed in a deactivated glass column and the IGC probes were injected at infinite dilution. The surface acid-base parameters were expressed in terms of the acceptor K-A and donor K-D parameters, analogous to the Gutmann acceptor and donor numbers derived from the Lewis concept of acids and bases. The K-A and K-D values were calculated from the experimental values of the enthalpy of desorption, corresponding to the specific acid-base interactions, and literature values of the acceptor and donor numbers for the acid-base probes, chloroform, carbon tetrachloride, ethyl acetate, and diethyl ether. Values of K-A and K-D suggest that the surfaces of cellulose, pine wood, and kenaf powder that have been washed by extraction with toluene/ethanol (2 : 1, v/v) are amphoteric, with a relatively greater capacity to accept electrons. The effect of the washing procedure on the dispersive component of the surface energy of the pine wood and kenaf powder was also determined. It was observed that the values for the washed substrates were relatively greater than those of the nonwashed counterparts.