The ignition delay times of mixts. contg. 35% n-heptane and 65% toluene by liq. vol. at room temp. (i.e., 28% n-heptane/72% toluene by mole fraction) were detd. in a high-pressure shock tube in the temp. range 620? T? 1180 K at pressures of about 10, 30, and 50 bar and equivalence ratios, j, of 0.3 and 1.0. The equation represents the data for j = 0.3 in the temp. range between 980-1200 K. At lower temps. no ignition was found at 10 bar within the max. test time of 15 ms, whereas for 50 bar, a reduced activation energy was obsd. A pressure coeff. of -1.06 was found for the data with j = 1.0. No common equation for the data at j = 1.0 could be found analogous to that for j = 0.3 because the ignition delay times show no Arrhenius-like behavior. A comparison with ignition delay times of n-heptane/air and toluene/air for j = 1.0 and 30 bar shows that the values of the mixt. of the two components are between the values of the single substances. Furthermore, the results confirm the neg. temp. coeff. behavior found for the mixts. at 30 and 50 bar, similar to n-heptane/air. A comparison for the other pressure and equivalence ratio values of this study was not possible because of the lack of data for pure toluene. These exptl. data were used in the development of a chem. kinetics model for toluene/n-heptane mixts. as described in a companion paper.