A pollen analysis was carried out on six herbaceous pollen types whose annual concentration represents a percentage higher than 0.3% in the atmosphere of the city of La Plata, Argentina, from July 1998 to June 2001. They are: Ambrosia, Cyperaceae, Chenopodiaceae-Amaranthaceae, Plantago, Poaceae and Urticaceae. Hourly patterns of the pollen types analysed with the intradiurnal daily index (IDI) could be grouped into three categories account the percentage that represent of pollen concentration registered during five hourly periods of the day. Group I includes pollen types that show a sharp peak in abundance gust one at hour of the day. Group II is formed by pollen types that show high concentrations in more than one hourly band during the daylight. Group III is characterized by the pollen types that show lower concentrations over a broad hourly band during the day.Facultad de Ciencias Naturales y Museo