A cooperative analysis of three triggered lightning flashes initiated during the Thunderstorm Research International Program (TRIP '81) at Langmuir Laboratory, New Mexico, has resulted in the determination of three-dimensional return stroke propagation speeds and peak currents for 56 subsequent strokes. We find a nonlinear relationship between the return stroke propagation speed and the stroke peak current that is qualitatively similar to that proposed by both Lundholm and Wagner. A nonlinear correlation is also found between the return stroke propagation speed and the dart leader propagation speed for 32 strokes. Linear correlation coefficients are evaluated for the following quantities; dart leader propagation speed and ensuing return stroke peak current (32 strokes: r=0.84); stroke peak current and interstroke interval (69 strokes; r=0.57); return stroke propagation speed and interstroke interval (56 strokes; r=0.49); dart leader propagation speed and interstroke interval (32 strokes; r=0.43). The weak positive correlation found between the dart leader propagation speed and the interstroke interval contradicts previous corresponding natural lightning observations. The mean three-dimensional return stroke propagation speed for 56 strokes is 12¿107 m/s with a range of 6.7¿107 m/s; the mean three-dimensional propagation speed found for 32 dart leaders is 20¿106 m/s with a range of 9.5¿106 m/s to 43¿106 m/s. The mean dart length measured is 50 m with a range of 15¿90 m. In two of the three flashes, the downward propagating dart leaders appear to meet upward propagating streamers at heights of approximately 20 and 30 m, respectively.