As regards effect of timing of medication on histamine induced contraction in isolated tracheal strips were more significant at night time pretreated groups. Considering effect of timing on bronchomotor response of histamine and branchorelxant effect of salbutamol were more at night time pretreated groups. As regards effect of timing of medication on pulmonary function tests they were also significant in nighttime treated groups. Considering effect of timing of drug administration on biochemical results all values of percentage reduction in urinary LTs, blood NO and Urinary NO were significant in nighttime treated groups.