An automatic wet-only precipitation collector was operated in the coastal forest of equatorial Congo for a complete seasonal cycle (November 1986 to September 1987). Inorganic (Na+, K+, NH+4, Ca++, NO-3, Cl-, SO=4) and organic (HCOO-, CH3COO-)ions were determined in 169 samples which represent 51 rain events. An average precipitation pH of 4.74 based on the volume weighted of H+ was obtained. Rain from stratiform clouds showed higher acidity (pH=4.62) than convective rainfall (pH=4.81). This acidity results from a mixture of mineral acids (64%, of which about 42% is HNO3) and organic acids (36%). Most of the HNO3 component can be attributed to the emission of nitrogen oxides from vegetation burning. To study the influence of variation in rainwater ion concentrations resulting from the differences in atmospheric liquid water content, rainfall events were stratified based on rainfall amount into convective and stratiform events. The seasonal variation in the chemical composition of these types of rain events allowed us to compare the relative seasonal importance of the different sources (terrestrial biogenic, marine, soils, and biomass burning). Comparison between precipitation chemistry in Congo and in Amazonia shows that the African equatorial forest is influenced by local fires and savanna fires in the southern hemisphere during the dry season and by fires in the northern hemisphere during the wet season. In Amazonia, on the other hand, the influence of biomass burning on rainwater chemistry appears to occur predominantly in the dry season. Since the precipitation collector subdivides rainfall events into 10 sequential samples, we examined the evolution in chemical composition and deposition during four large convective events. The results demonstrate the washout of ions at the onset of precipitation producing higher rainwater concentrations and their dilution as the rainfall intensity increases. ¿ American Geophysical Union 1992