ABSTRACT: Comparative estimates of the leaf area index (LAI) of a mangrove forest canopy in Peninsular Malaysia were obtained by 3 independent methods: (1) from direct measurement of canopy leaf area above a prescribed ground area; (2) from simple measurements oflight flux density above and beneath the canopy; (3) from measurements of direct beam transmittance through the canopy. Measurements were also made of the rate of net photosynthesis at different levels in the canopy. LAIs obtained by direct measurementranged from 2.2 to 7.4 over 4 replicate 0.25 m² quadrats, with a mean of 4.9. This high degree of variability was attributed partly to the small quadrat size and partly to the spatial heterogeneity of the canopy. In contrast, estimates of LAIobtained from log averaged measurements of light transmission over a larger area of forest varied by less than 5% between replicates, with an average of 5.1. Measurements of direct beam transmittance yielded an average canopy LAI of 4.4. Average rates ofnet photosynthesis ranged from 4 µmol CO₂ m^-2 s^-1 at the bottom of the canopy to about 10 µmol CO₂ m^-2 s^-1 at the top of the canopy. The LAI weighted average rate of net photosynthesisintegrated over the entire canopy was 9 µmol CO₂ m^-2 leaf s^-1. Assuming an effective daylength of 8 h, total daily net photosynthetic carbon fixation was estimated to be 155 kg C ha^-1 d^-1, giving anannual net photosynthetic production of 56 t C ha^-1 yr^-1. This is substantially higher than previously reported for mangrove forests.