Changes in composition of volatiles released by freshly-felled specimens of different softwood and hardwood species after incubation at sub-tropical temperatures and high humidity have been determined by gas chromatographic and spectrophotometric techniques. A method is described for the isolation, identification and quantitative assay of organic acids, alcohols and esters released to atmosphere from selected wood species under certain exposure conditions. Sweet chestnut (Castanea sativa), oak (Quercus robur), wych elm (Ulmus glabra) and Douglas Fir (Pseudotsuga taxifolia) heartwood and wych elm sapwood all released significant quantities of acetic acid (1600-550 p.p.m. of dried wood) and of formic acid (200-40 p.p.m. of wood as dried) when incubated for 6 months at 48° and 100per thousand R.H., but Norway spruce (Picea abies) and beech (Fagus sylvatica) heartwood and sapwood and Douglas Fir sapwood on the other hand released only small quantities of acids. The main neutral volatiles indentified after incubation were methanol, methyl acetate, ethanol, formaldehyde and an unidentified component. Sterilisation of wood shavings with propylene oxide prior to incubation significantly reduced the concentrations of formic acid, acetic acid and methanol, with accompanying increases in ester concentration. This may be due to inhibition of enzymic hydrolysis of simple esters in sap fluids and of polymeric esters in the wood cell-wall substance.