The study began with a screening visit. All subjects had physician-diagnosed asthma. All performed a baseline set of lung function measurements. They entered a 2-week run-in period during which they kept a diary of peak flows, asthma symptoms, and beta agonist use. Subjects were instructed in peak flow technique and asked to perform three maneuvers each time. The maneuver was considered technically sufficient if the variation in the values obtained on the three attempts are with 10% of each other, and the highest value was recorded in a diary. Subjects whose diaries were > 80% complete entered the study and were randomly assigned to active treatment or placebo. Spirometry was repeated. Blood was taken for fatty acid composition of plasma and leukocytes, LT generation, and DNA for genotyping at the LTC4S locus. Subjects were provided with peak flow diaries, instructed in the appropriate performance or peak flow maneuvers, and asked to record morning and evening peak flow each day (reflecting the best of three efforts each time). After three weeks of treatment, diary cards will be collected and spirometry repeated. After six weeks of treatment, blood was drawn for safety monitoring, for measurements of fatty acids in plasma and leukocytes, and for the functional analyses. Spirometry was repeated. Subjects then entered a six-week washout period. Two weeks before the end of this period they again started to keep diary cards. At the conclusion of the 6-week washout period they entered the cross-over treatment phase (six weeks) which followed the same protocol as the first treatment period with assessment of fatty acid analyses, cellular function studies, safety monitoring, and spirometry. Pregnancy testing was performed before and after each treatment period. Dairy cards (with peak flow monitoring results) will be collected at each visit (3 week intervals during the placebo and active treatment arms of the study).