Through a research in the area of the Parque Zoobotânico of Universidade Federal do Acre (Rio Branco, Acre, Brazil) between September, 1983 and August, 1984 the Chibui bari Righi & Guerra, 1985 activity in secondary vegetation is analysed In fifty squares measuring fifty centimeters each side, the casts present in their Interior were collected once a fortnight. The changes of the pH, the moisture and temperature o f the soil were determined throughout the period of study. In this region the earthworms activity is Limited to the rainy season or winter (from November to May). This activity is controlled only by the soil moisture since the temperature and pH do not present relevant variations throughout the year. The burrowing, the copulation and the hatching of cocoons are performed during this period. By the end of the rainy season, the worms enter in aestivation at the depth of about one meter and remain this way until the beginning of the next winter. The cast production, also analysed, was about 80 t/ha /year the maximun production in the area of study, an intermediate measure among the results obtained In other tropical ecosystems.