Background: The effects of environmental factors and ambient concentrations of grass pollen on allergic asthma are yet to be established. Objective: We sought to estimate the independent effects of grass pollen concentrations in the air over Melbourne on asthma hospital admissions, for the 1992-1993 pollen season. Methods: Daily grass pollen concentrations were monitored over a 24 hr period at three stations in Melbourne. The outcome variable was defined as all-age asthma hospital admissions with ICD9-493 …