4-week study to assess asthma control as measured by lung function and clinical features, rhinitis treatment, subject-rated overall satisfaction with treatment, and safety outcomes when FLONASE™ 200mcg (FPANS) QD, Singulair 10mg (MON) QD, or placebo QD is added to ADVAIR™ DISKUS™ 100/50mcg (FSC) BID and when Singulair 10mg (MON) QD is added to placebo DISKUS BID in adolescent and adults subjects. Male or female subjects must be symptomatic with both seasonal allergic rhinitis and persistent asthma, and have an FEV1 65-95% of predicted while using an as-needed short-acting beta2-agonist or an allowed ICS or non-ICS controller therapy. Subjects will replace their short-acting beta2-agonist with VENTOLIN™ HFA (for rescue) and will enter a 7-14 day run-in period during which they will continue use of their pre-study controller therapy. At Visit 2, subjects who meet both the asthma and rhinitis randomization criteria will be randomized to double-blind treatment with ADVAIR DISKUS 100/50mcg BID and either FLONASE 200mcg QD, Singulair 10mg QD, or placebo QD, or to placebo DISKUS BID and Singulair 10mg QD. The co-primary efficacy measures will be the mean change from baseline at endpoint in AM PEF, compared between the FSC and the MON treatment groups to assess superiority and compared between the FSC and FSC+MON treatment groups to assess equivalence. Secondary efficacy measures for rhinitis will be mean change from baseline in subject-rated daytime total nasal symptom score and nighttime total nasal symptomatic score averaged over Weeks 1-2 (D-TNSSW1-2 and N-TNSSW1-2, respectively). Secondary efficacy measures for asthma will be mean change from baseline at endpoint in morning pre-dose FEV1, percentage of symptom-free days, and percentage of rescue-free days. Other measures will include subject-rated overall satisfaction with treatment, evening PEF, asthma symptom scores (D-INSSW1-x, N-INSSW1-2), averaged over Weeks 1-2. Descriptive measures will include all total and individual nasal symptoms scores averaged over Weeks1-4. Safety measures will include assessment of clinical adverse events and asthma exacerbations.