Pollen rain in mountain forests of Tucuman Province, Argentina. This study is referred to water dynamics in the mountain forests of Tucuman Province, (Argentina) started in 2002 at the Instituto de Ecologia of the Fundacion Miguel Lillo. The place selected was the Toma del Rio Horqueta, Reserva de La Florida (Dept. Monteros) over 1300m.s.l. A pluviometer, considered as a device similar to a captator Tauber, was used in order to measure water accumulated twice, or sometimes once a month. Water gathered during a year (July 2004 - June 2005) was centrifugated and its sediment was processed according to conventional methods in order to ascertain the content of pollen rain in the mountain forests. More than 50 taxa were identified showing the natural vegetation of the area. A pollen calendar was elaborated with these data. Two periods of significant pollen contribution were observed. The first period, in September, showed different pollen types among wich the following arboreal species predominated: Alnus acuminatus, Juglans australis, Polylepis australis, Prunus tucumanensis, Parapiptadenia excelsa, Celtis sp. and Myrtaceae. The second period, in December, was characterized by a high percentage of Ulmaceae. A third period, although less important was also observed in April, with the dominance of Asteraceae. Other species appeared in small quantities according to their time of blossom.