In vitro studies indicated anaerobic that highest nitrogenase activity in River Estate loam was achieved with 2 per cent glucose added under anaerobic conditions. Activity in the roots of Digitaria umfolozi also increased with decreased oxygen partial pressure. When nitrogenase activity was assessed by the acetylene reduction method in 31 disturbed soils and 28 types of vegetation of Trinidad and Tobago, most soils showed relatively little or no activity even when supplemented with glucose. Many roots showed similar levels of nitrogenase activity although in a few instances activity as high as 688 nmol C2H4/h/g root was achieved. Assayed undisturbed soil cores of paddy (wetland rice) and swamp soils showed very high nitrogenase activity although those containing Digitaria sanguinalis showed higher activity.