Allergic diseases such as bronchial asthma, allergic rhinitis and atopic dermatitis are dramatically increasing all over the world including developing countries like India. Today, more than 30 % of the population is known to suffer from one or other allergic ailment. Major causative agents implicated are pollen grains, fungal spores, dust mites, insect debris, animal epithelia, etc. Several aerobiological studies have been conducted in different parts of the country to ascertain aerial concentration and seasonality of pollen grains and fungi. Recently, an "All India Coordinated Project on Aeroallergens and Human Health" was undertaken to discover the quantitative and qualitative prevalence of aerosols at 18 different centres in the country. Predominant airborne pollen are Holoptelea, Poaceae, Asteraceae, Eucalyptus, Casuarina, Putanjiva, Cassia, Quercus, Cocos, Pinus, Cedrus, Ailanthus, Cheno/Amaranth, Cyperus, Argemone, Xanthium, Parthenium and others. Clinical and immunological evaluations have revealed allergenically important texa - some of them for the first time. Allergenically important pollen are Prosopis juliflora, Ricinus communis, Morus, Mallotus, Alnus, Querecus, Cedrus, Argemone, Amaranthus, Chenopodium, Holoptelea, Brassica, Cocos, Cannabis, Parthenium, Cassia and grasses. Further cross-reactivity of the IgE antibodies is a common phenomenon among various pollen allergens. Ricinus communis pollen from commonly growing weeds in India, cross-reacts with latex (Hevea brasiliensis), Mercurialis annua and also with seeds of Ricinus communis - all belonging to family Euphorbiaceae. Areca catechu cross-reacts with other members of Arecaceae such as Phoenix sylvestris, Cocos nucifera and Borassus flabelifer. Several reports on pollen and fruit syndrome have been analyzed. Experiments conducted by us revealed that pollutants (NO(2) and SO(2)) not only affect pollen morphology but also changes their allergenic potency. Immunotherapy with recombinant proteins having similar epitopes from different allergens have been advocated, besides allergen avoidance.