Parthenium hysterophorus, a recently invaded toxic weed, in Eastern India, is now growing gregariously in Salt Lake City — a newly developed township situated in the eastern fringe of the metropolitan city of Calcutta. The floristic survey revealed that most of the trees and shrubs in Salt Lake City have been introduced except for a few, which were recorded as natural occurrence,Partheniumbeing most prevalent among them. Ecological associations ofPartheniumin various localities of Salt Lake City were also investigated. Aerobiological survey was done using a Burkard seven day Volumetric Spore Trap, with the object to record the occurrence ofPartheniumpollen in the air of Salt Lake in different seasons along with other airborne types. A total of 45 pollen and 60 fungal spore types were trapped and recorded. The frequency of grass and cyperaceous pollen were found to be dominant followed byTrema. Frequency ofPartheniumwas relatively insignificant. Chemical analyses of the pollen grains ofPartheniumincluding assay of carbohydrate, lipid, protein, etc., were done. Clinically one out of six patients showed ELISA positive reaction toPartheniumpollen.