The combination reactions CCl3 + CCl3 (+ M) --> C2Cl6 (+ M) and CCl3 + Br (+ M) --> CCl3Br (+ M) (with rate constants of k(1) and k(2), respectively) were studied at temperatures of 250 and 300 K over the pressure range of 0.01-1000 bar. Helium, argon, xenon, N-2, CO2, and SF6 were used as bath gases. CCl3 radicals were generated via the photolysis of CCl3Br at 248 nm, and their absorption was monitored at 223.5 nm. The limiting "high-pressure" rate constants within the energy-transfer mechanism were determined, independent of density and the choice of the bath gas, over the pressure range of 1-10 bar, to be k(1,infinity)(T) = (1.0 +/- 0.2) x 10(-11) (T/300 K)(-0.17) cm(3) molecule(-1) s(-1) and k(2,infinity)(T) = (2.0 +/- 0.2) x 10(-11) (T/300 K)(-0.13) cm(3) molecule(-1) s(-1). In the helium, N-2, and argon bath gases, at pressures above similar to40 bar, the reactions became increasingly faster when the pressure was further raised until they finally started to slow at densities where diffusion controlled kinetics dominates. This is the first detailed report of such a peculiar density dependence of combination rate constants for larger radicals with five or eight atoms. Possible origins of these pressure effects, such as the influence of the radical-complex mechanism and the density dependence of electronic quenching, are discussed.