Economic evaluations of pharmaceuticals are increasingly being conducted in conjunction with randomized phase III clinical trials to meet the demand for pharmacoeconomic data when new products are launched. While the need for such data is often global, the trials in which relevant information may be collected are often conducted in only one or a limited number of countries. A critical issue is how data from pivotal clinical trials in one setting can serve as the basis for pharmacoeconomic evaluations in others. We address this issue and report on four economic evaluations that we undertook in conjunction with a recent U.S. phase III clinical trial of recombinant human deoxyribonuclease (rhDNase), which is used to improve pulmonary function in patients with cystic fibrosis (CF). The objective of these evaluations was to estimate the potential impact of rhDNase therapy in France, Germany, Italy, and the United Kingdom on the direct costs of medical care for the treatment of respiratory tract infections (RTIs) in patients with CF. Analyses of economic impact were undertaken both with and without adjustment for differences in practice patterns between the United States and the countries of interest. Our findings suggest that rhDNase therapy may reduce the cost of RTI-related care by between US$600 and US$1,100 over a 24-week period; the cost of rhDNase is not included in these figures, as a price was unavailable when our analyses were undertaken. Despite methodologic challenges, economic evaluations that meet the information needs of decision makers in diverse countries can nonetheless be undertaken in conjunction with phase III clinical trials.