Substantial observational, non-experimental evidence suggests that paracetamol use may be a novel risk factor for asthma. Paracetamol is widely used in NZ children and the evidence provided by a RCT in infants will show if paracetamol causes asthma. Our proposed main study is a randomised, open-label, parallel groups RCT of whether paracetamol use (as required for fever and pain in infants), following admission to hospital for bronchiolitis, increases the risk of wheeze and atopy at age 3. The feasibility study will establish the consent rate in this group and the comparator group with the highest recruitment rate: placebo, ibuprofen or restricted use of paracetamol. The parents/guardians of infants admitted with bronchiolitis to Wellington Hospital will be interviewed. 50 infants will be randomised to liberal or restricted paracetamol and followed for three months to allow testing of the utility of phone follow-up, diary return, and assessment methods of medication use.