In Japan, pulmonary thromboembolism (PTE) is rare and the therapy of this disease, especially the thrombolytic therapy, has not been established yet. We studied the effect of thrombolytic therapy by urokinase (UK) in eighteen patients with PTE. We also compared the results with those in Europe and the United States. Eighteen patients (male 7, female 11) were 27 yo to 77 yo (mean 55 yo). Seven cases were mild and 11 cases were moderate to severe. The initial dosage of UK administration was 2.4 x 10(5) to 7.2 x 10(5) IU with the mean of 4.1 x 10(5) IU, which was approximately the double of those in Europe and the US. The duration of UK therapy was 1 to 9 days with the mean of 4.8 days. It was longer than in Europe and the US (12-24 hours). Total amount of UK in each case ranged 4.8 x 10(5) to 42 x 10(5) IU (mean 19.3 x 10(5) IU) with the daily dosage of 4.0 x 10(5) IU in average. They were almost half of those in Europe and the US. Clinical signs and laboratory findings subsided in 1-7 day by UK administration in 14 cases (87%) with the reduction of defects on perfusion lung scans and all of these cases survived. No severe complications were found in any cases. We conclude that the thrombolytic therapy with UK in Japan might be acceptable from the results of this present study. However, the prospective study of thrombolytic therapy on a larger scale remains to be done in the future.