21 ambulatory patients with acute or chronic pain localized to the chest, were treated successfully by continuous intercostal block. They included 6 women and 15 men, aged 39-70. Treatment was initiated in the outpatient clinic and continued at home for usually 5-6 days. Between 15-20 ml of 0.5% marcaine were continuously injected over the course of 6-12 hours through a catheter introduced into the intercostal space by a Touhy needle. 76% of the patients had substantial relief of pain during the block and required only minimal systemic medication. During a 3 month follow-up after cessation of the block, up to 65% were still pain-free. Results were poor or only fair in those with malignancy and long-standing intercostal neuralgias. There were no serious side-effects during treatment. This method is an important new tool in the treatment of pain.