The number of clinic consultations for condylomata acuminata (genital warts) has increased substantially during the last 30 years. Most infections produce benign lesions but a few types may be associated with cervical and penile cancers. Interferons (IFN) have shown antiviral properties to these infections and IFN-beta in particular has demonstrated a specific cytopathic effect in humans. A total of 124 patients with condylomata acuminata, the majority of whom had failed previous therapy, were treated intralesionally with either recombinant human interferon-beta la (r-hIFN-beta-1a) or placebo. Up to 6 lesions were treated in each patient, and injections were made 3 times per week for a total of 9 injections. The patients were then followed up for 3 months. Efficacy assessments at all time points (day 19, week 6 and month 3) showed a clear advantage for the r-hIFN-beta-1a interferon-beta treatment. Patients receiving r-hIFN-beta-1a showed a greater proportion of treatment success in terms of the complete or partial reduction (at least 50%) of the total area of the treated lesions. The treatment was also well tolerated. Headache, flu-like symptoms and asthenia were more common in patients receiving r-hIFN-beta-1a, but these adverse events were generally mild in severity and rarely led to patient withdrawal. It was concluded that r-hIFN-beta-1a has good efficacy in condylomata acuminata, and therefore presents a useful therapeutic alternative in this hard-to-treat condition.