The role of fine root dynamics in the carbon and nutrient cycles of a primary, lowland dipterocarp rain forest in Sabah, Malaysia was investigated. A new method for estimating fine root production was developed which involved the combination of excavation and rhizotron techniques to separately quantify spatial and temporal variability in the root system. The aim was to produce a method that could quantify the simultaneous occurrence of fine root production, mortality and decomposition. The biomass of roots ^2, >2-5-^10, >10-^15 mm diameter in the top 1.2 m of the soil was 2830, 3544, 2310, 2157 kg ha ‘ respectively. Fine root (