This 8 arm study will evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of single ascending doses of R1671 or placebo in patients with mild, intermittent, asymptomatic asthma. Patients will be randomized to receive placebo or R1671, at a starting dose of 0.0015mg, by intravenous infusion; this dose will be escalated in subsequent groups of patients after a satisfactory assessment of the data from the previous dose. The anticipated time on study treatment is <3 months, and the target sample size is <100 individuals.