OBJECTIVE To determine the effect of oseltamivir (75mg twice daily) on time to return to baseline health, sleep and activity in patients with laboratory-confirmed influenza infection. PATIENTS AND METHODS Data from 1642 otherwise healthy adults (aged 13-64 years), who had experienced a febrile influenza-like illness (>38 degrees C) of up to 36 hours' duration together with at least one respiratory and one systemic/constitutional symptom, were pooled from four randomised, double-blind, placebo-controlled clinical trials. Patients in these trials had been randomised to receive either oseltamivir or placebo for 5 days and had been allowed unlimited use of symptom-relief medications. The primary analysis examined the effect of oseltamivir treatment on patients' general health status, sleep and normal activities as measured by visual analogue scales. Secondary analyses examined the possible effects of gender, influenza type, smoking, employment status and time to treatment (< or = or >24 hours) on these endpoints. RESULTS Oseltamivir significantly reduced the time taken to return to baseline health, sleep and activity across all pooled patients (p < 0.0001) and increased the proportion of patients returning to full activity within the first 7 days following treatment start. Gender, smoking status, time to treatment, influenza subtype and employment status had no appreciable effect on the effectiveness of oseltamivir. CONCLUSIONS In otherwise healthy adults, oseltamivir reduces the time to return to pre-illness levels of health, sleep and activity, and may help to decrease the overall burden of influenza on society. This provides an important rationale for the early use of antiviral treatment, such as oseltamivir, for the treatment of influenza in otherwise healthy adults and adolescents.