Past studies have reported an increased risk of developing sensitisation to allergens for babies born in months of high allergen levels, but these studies had no information about allergen exposure or place of birth. It has been suggested that the most sensitive period for developing allergic sensitisation is the first three months of life, corresponding to a physiological trough in serum immunoglobulin levels. (Kemp, 1979). Aim: To determine if children born in the 3 months following peak seasons for dust mite (HDM). .\liernaria and grass pollen are at significantly more risk of developing sensitisation to these allergens than children born during the rest of the year. Methods: Population samples of children aged 7-12 years born in either Moree (n=3111 or Wagga Wagga (n=640) were given a skin prick test for atopy to aero-allergens (wheal size of 3mm) in 1997. Seasonal variation in \lternaria and pollens were determined from daily counts measured by burkard spore traps in both towns during 1997 and 1998. Concentration of HDM allergens in children's homes were measured in different seasons. Children born in the 3 months following peak allergen seasons were compared to those born in the rest of the year. Results: Table: Odds Ratios (95% CI) for atopy associated with peak allergen seasons. Atopy Moree Wagga Wagga HDM 0.74(0.43-1.28) 0.89(0.61-1.30) Alternaria 0.72(0.35-1.48) 0.87(0.56-1.38) Pollen 0.60(0.34-1.07) 1.27(0.81-1.99) Conclusion: This study does not support the hypothesis that allergic sensitisation to HDM. Alternaria or grass pollen could be related to season of birth.