The dissociation of diacetyl dilute in krypton has been studied in a shock tube using laser schlieren densitometry at 1200-1800 K and reaction pressures of 55 +/- 2, 120 +/- 3, and 225 +/- 5 Torr. The experimentally determined rate coefficients show falloff and an ab initio/Master Equation/VRC-TST analysis was used to determine pressure-dependent: rate coefficient expressions that are in good agreement with the experimental data. From the theoretical calculations K-infinity(T) = 5.029 x 10(19) (T/298 K)(-3.40) exp(-37665/T) s(-1) for 300 < T < 2000 K. The laser schlieren profiles were simulated using a model for methyl recombination with appropriate additions for diacetyl. From the Simulations rate coefficients were determined for CH3 + CH3 = C2H6 and CH3 + C4H6O2 = CH3CO + CH2CO + CH4 (k(T) = 2.818T(4.00) exp(-5737/T) cm(3) mol(-1) s(-1)). Excellent agreement is found between the simulations and experimental profiles, and Troe type parameters have been calculated for the dissociation of diacetyl and the recombination of methyl radicals.