The rate constants for the gas-phase reactions of ozone with the biogenic hydrocarbons isoprene, alpha- and beta -pinene, and limonene were measured using the relative rate technique over the temperature range 242-363 K and at 760 Torr total pressure. Helium was the diluent gas, and the reactants were detected by on-line mass spectrometry. The following Arrhenius expressions have been determined for these reactions (in units of cm(3) molecule(-1)s(-1)): isoprene, (10.9(-2.17)(+2.70)) x 10(-15) exp[-(1998 +/- 63)/T]; alpha -pinene, (0.48(-0.18)(+0.29)) x 10(-15) exp[-(530 +/- 150)/T]; beta -pinene, (1.74(-0.36)(+0.46)) x 10(-15) exp[-(1297 +/- 75)/T]; and limonene, (2.95(-0.61)(+0.77)) x 10(-15) exp[-(783 +/- 72)/T]. The Arrhenius parameters determined here for the reactions of ozone with beta -pinene and limonene are the first to be reported.