The physical features, climate, history and vegetation of the Olokemeji Forest Reserve are described. There are two main types of typical vegetation in south-western Nigeria, both of which are present in the reserve moist semi-deciduous forest, which is the climatic climax for the area, and derived savanna woodland, which is a biotic fire climax. The derived savanna and the secondary nature of the forest are due to previous cultivation. A research site in the typical dry type of moist semi-deciduous forest had more or less complete strata at heights of 18-23 m, 10-14 m and 4-9 m and a con-tinuous herb stratum. The floristic composition was very mixed. The site was probably last farmed during the third quater of the 19th century. The canopy on the research site in the derived savanna woodland varied from complete to open. There were incomplete strata at heights of 4-8 m and 1.5-4 m and a herb stratum largely composed of grasses. Ninety-five per cent of the forest species and 30% of the savanna species were phanerophytes. Half the savanna plants were hemicrypto-phytes and many were therophytes. There were many geophytes on the savanna site and some on the forest site. Twenty-seven per cent of the forest species (almost entirely woody plants) and 5% of the savanna species (all herbs) were climbers. The taller forest trees were mainly deciduous and the smaller trees were increasingly evergreen. All the savanna species were deciduous. The bark of the savanna trees was generally over three times as thick as that of the forest trees. Most leaves from both sites had the following characters. They were mesophylls or microphylls (many savanna herb leaves were nanophylls), had a "maximum circle diameter" between 27 and 81 mm, a length/width ratio between 2 and 20, were unlobed and had entire margins. The leaves of savanna monocotyledons were exceptions in that they mostly had a "maximum circle diameter" between 3 to 9 mm and a length/width ratio between 20 and 200. Eighty per cent of the forest species, com-pared with 15% of the savanna plants, had drip tips and these were about twice the length of the savanna drip tips. Most woody plants on both sites had a deep tap root with subsidiary roots growing horizontally and mainly 10-20 cm below the soil surface. The soil was predominantly loamy, rather sandy on the forest site, and rather silty and clayey on the savanna site.