In order to assess the influence of change in land use on microbial activity, soils from the A horizon of two major wet tropical forests (moist deciduous (MD) and semi-evergreen (SE)) and two adjacent plantations of padauk (Pterocarpus dalbergioides) and teak (Tectona grandis) established by clearing portions of these forests were studied for various microbial indices and their interrelationships. The two sites revealed marked differences in soil organic matter and microbial properties. The levels of microbial biomass C, biomass N, basal respiration, ergosterol and adenylates (ATP, AMP, ADP) at the forest sites significantly exceeded the corresponding values at the plantation sites, indicating greater microbial activity under the former. Among the ratios of different microbial properties, the ergosterol-to-biomass C ratio and mean metabolic quotient (q(CO2)) were significantly higher under the forests suggesting a marked decline due to deforestation and cultivation. The ergosterol-to-biomass C ratio further indicated that the fungi, especially at the plantation sites, have very low ergosterol content. The ratios of biomass N-to-total N, biomass C-to-N, biomass C-to-organic C, and ATP-to-biomass C, however, did not vary significantly between the forest and plantation sites. On the contrary, adenylate energy charge (AEC) levels at the forest sites were consistently higher than 8.0, reflecting greater microbial proliferation at these sites. Overall, our study indicated that on a long-term basis, deforestation and cultivation significantly reduced microbial activity due to decline in available organic matter/substrate levels. © 2003 Elsevier B.V. All rights reserved.