Decomposition of coniferous litter was studied from March 1990 until March 1991 in a pine forest plantation (Pinus merkusii) in two 0.2 ha plots, at altitudes of 600 and 800 m on the southwest slope of Mount Merapi (2911 m), Central Java. Stratified litterbag sets were used to compare the influences of seasonality and degradation stage on the decomposition of pine litter. The variables used in monitoring the decomposition processes were weight loss, carbon and nitrogen contents and enzyme activity of the litter microflora. At each site the litterbags containing pine needles from L and F layers were randomly distributed in the L and F layers, respectively. After 1 year the weight loss in the litterbags in the upper plot was 32% in the L and 53% in the F layer. Weight loss in the lower plot was 60% in the L and 42% in the F layer. Temperature and moisture were not responsible for these differences in weight loss. Carbon content of litter in both plots decreased during a year from 49 to 35-37% in the L layer and from 38 to 28-31% in the F layer. Net immobilization of N took place in the L layer and net mobilization in the F layer. Dehydrogenase activity was positively correlated with N content and was highest when the critical N % was reached. Decomposition rate was influenced by moisture, but the chemical composition of the litter seemed to be even more important in determining the decay rate of the L layer.