An investigation was conducted to compare differences in chemical characteristics of Costa Rica soils under continuous cultivation and under forest vegetation. Inceptisols from young volcanic material under forest, sugar cane, coffee and pasture, respectively, were sampled in the San Carlos region of Costa Rica, and analysed for pH, organic matter, N, Ca, Mg, K, Na, Al, Fe, Zn and Mn contents. Indications were obtained that continuous cropping for 1 to 22 years with sugar cane resulted in a decrease in Ca and Mg content and an increase in acid extractable Al concentrations, compared to amounts found in forest soils. In soils under coffee the only significant changes were a reduction in soil organic matter, N and Al contents. Exchangeable bases decreased slightly during the first two years, but in fields 15 years under coffee, the content of exchangeable bases was affected slightly, except for a relatively marked decrease in amounts of Mg. Conversion into pasture maintained soil fertility at a level comparable to that found in the forest soil ecosystem. It was concluded that differences in vegetational ecosystems caused soil chemical changes, but deforestation in the tropics did not necessarily result in rapid soil degradation processes. The magnitude of the data showed that the soil in the San Carlos region of Costa Rica had been cultivated for at least 10 to 20 years without producing evidence of excessive deterioration.