SummaryPreparatory to the use of volatile oils in systematic studies of Australian rainforest trees, the extent and systematic significance of seasonal variation in volatile oil composition were studied. Monthly samples were taken from eight trees of Lauraceae, representing six genera, over a period of 14 months; three of these trees wereLitsea leefeana. It was found that the patterns of variation shown by these trees over the sampling period varied between trees, and in each case appeared to be unrelated to any seasonal trend. An analysis of the variation within the three trees ofLitsea leefeanashowed only seven compounds varying significantly by month of sampling, while 65 varied significantly by tree. Of the former, only one compound exceeded 0.5%. These three trees remained clearly distinct in any multivariate analysis. Monthly samples taken from a tree ofSyzygium canicortex(Myrtaceae) over a period of 13 months were compared with single samples from nine other trees of this species. It was found that the variation within the one tree over the seasonal sampling period was less than the variation between trees. Thus it is concluded that seasonal variation presents no problems for sampling of Australian rainforest trees for volatile oil composition, and that samples can be taken at any time of the year.