The kinetics of the isoprene-OH/OD reaction in the presence of O-2 and NO have been studied using laser photolysis/laser-induced fluorescence. We report pressure and temperature-dependent rate constants for the addition of OH/OD to isoprene are in good agreement with previous studies. On the basis of simulations to OH cycling curves, we find a value of (9.0 +/- 3.0) x 10(-12) molecule(-1) cm(3) s(-1) for the overall reaction rate constant of hydroxy peroxy radical with NO at 298 K. We report a rate constant for 02 addition to the hydroxy alkyl radical of (2.3 +/- 2.0) x 10(-12) molecule(-1) cm(3) s(-1) at 298 K. We find little generation of OH from the OD initiated oxidation of isoprene, and no significant differences in OH and OD cycling, suggesting that H-shift isomerization is the major pathway for delta-hydroxy alkoxy radicals, in agreement with theoretical predictions.