In a placebo‐controlled, randomized, and double‐blind 1–day field study, the efficacy and onset of action of capsule acrivastine 8 mg were evaluated in 42 patients suffering from allergic rhinoconjunctivitis elicited by natural grass pollen exposure. Before and for 2 h after treatment, the patients scored the severity of five rhinoconjunctivitis symptoms every 10 min on a 0–5 scale (0 = no symptoms; 5 = very severe symptoms). The number of sneezes was recorded, and every 30 min, measurements of nasal peak flow were made. Before treatment, there was no difference in median total symptom score (mTSS) between the acrivastine group (A) and the placebo group (P) (12 and 12, respectively). Time of onset was estimated by an exponential decay model to be 19 min (95% confidence interval 0–39 min). A statistically significant difference in percent reduction of mTSS between A and P was observed for the first time 46 min after treatment start (A = 22%, P = 0%, P <0.05). A 50% reduction in total symptom score (TSS) was achieved within 60 min by 38% in A and 17% in P (NS), and within 80 min in 52% and 17%, respectively (P <0.05). The median time for 50% reduction in TSS (MT50) was 80 min for A and > 120 min for P (P <0.01). The symptom score of sneezing and number of sneezes were evaluated for periods of 30 min. The difference between A and P became statistically significant from 31–60 and 61–90 min, respectively (P <0.05 and P <0.01). Objective and subjective determinants in the different time intervals were well correlated. Improvement of nasal congestion was observed in A at 91–120 min, as measured by nasal peak flow.