Twelve courses of intravenous temocillin were given in combination with an intravenous aminoglycoside to five patients with cystic fibrosis (CF) for pulmonary exacerbations associated with Pseudomonas cepacia. All patients were infected concurrently with Pseudomonas aeruginosa in addition to P. cepacia. Improvement occurred after six of seven courses given to three patients in which temocillin was used as first-line therapy and following three of five courses given to two patients after failure of other antipseudomonal agents. All ten pre-treatment isolates of P. cepacia were resistant to aminoglycosides and eight were sensitive to temocillin. Clinical improvement was seen on both occasions in which the pre-treatment isolates were resistant to temocillin.