1. A method of treating pulmonary hypertension comprising: administering by inhalation to a human suffering from pulmonary hypertension a therapeutically effective single event dose of a formulation comprising from 200 to 1000 .mu.g/ml of treprostinil or a pharmaceutically acceptable salt thereof with a pulsed ultrasonic nebulizer that aerosolizes a fixed amount of treprostinil or a pharmaceutically acceptable salt thereof per pulse, said pulsed ultrasonic nebulizer comprising an opto-acoustical trigger which allows said human to synchronize each breath to each pulse, said therapeutically effective single event dose comprising from 15 .mu.g to 90 .mu.g of treprostinil or a pharmaceutically acceptable salt thereof delivered in 1 to 18 breaths.

1. A kit for treating pulmonary hypertension comprising: (i) a formulation comprising 200 to 1000 .mu.g/ml treprostinil or a pharmaceutically acceptable salt thereof; (ii) a pulsed ultrasonic nebulizer comprising an opto-acoustical trigger, configured to (a) aerosolize a fixed amount of treprostinil per pulse, and (b) deliver by inhalation a therapeutically effective single event dose of said formulation, said single event dose comprising 15 .mu.g to 90 .mu.g treprostinil or a pharmaceutically acceptable salt thereof delivered in 1 to 18 breaths; and (iii) instructions for using the pulsed ultrasonic nebulizer with the formulation to treat a patient with pulmonary hypertension by delivering 15 .mu.g to 90 .mu.g treprostinil or a pharmaceutically acceptable salt thereof in 1 to 18 breaths to the patient in the single event dose.