False-colour scanning electron micrograph (SEM) showing pollen grains from the ragweed, Ambrosia psilostachya, one of the allergens which can cause hay fever (pollenosis) in susceptible individuals. Hay fever is the commonest of all allergic conditions, occuring when certain pollens or mould spores are inhaled. Persons suffering from hay fever produce a sensitising antibody, immuno- globulin E (IgE), which is present on the surface of cells in the nose & eyes. When this antibody encounters an allergen, chemicals known as histamines are released, producing swelling & inflammation of the linings of the nose, eyes & throat. Magnification: x1800 at 6x6cm size.