Selected ro-vibrational states (v′,J′) of excited Br2B3Π(0u+) were populated by absorption of radiation (570–600 nm) from a single-frequency c.w. dye laser, or from a 1 pm bandwidth pulsed dye laser. The rates of electronic, vibrational and rotational energy transfer within the B state of Br2 were studied, using Br2, Ar, He, N2 and Cl2 as collision partners. Wavelength-resolved fluorescence was analysed in the c.w. excitation studied. The results showed that Ar and N2 possessed large cross-sections for R–T transfer, whilst electronic quenching was slow. Collision efficiency of N2 for V–V transfer in Br2(B, ν′= 11–15) was ≈0.1, with Δv=+1 slower than Δv=–1. Minimal coupling of R–T and vibrational transfer in collisions with N2 found. When Δv′ quantum jumps occurred in vibrational transfer with N2, conservation of rotational quantum number J′ was observed, with a small amount of broadening of the initial rotational distribution. Collisions of Br2(B) with Br2(X) resulted in efficient electronic deactivation, with very little observed ro-vibrational energy transfer. Time-resolved undispersed fluorescence was analysed in the pulsed excitation studies. The rate constant for electronic self-deactivation of Br2(B, ν′= 14) was (4.2 ± 1.3)× 10–10 cm3 molecule–1 s–1 at 298 K. Electronic deactivation is assigned to collisional predissociation, which thus has a high efficiency. The results are interpreted in terms of a large cross-section for R–T transfer in collisions of Br2(B) with rare gas atoms, which lead to collision-induced predissociation and thus to depletion of Br2(B) population. Collisions with Cl2 also were found to give rapid collisional depletion of Br2(B). The elementary processes responsible in this case are probably a combination of electronic deactivation and rovibrational energy transfer, leading to predissociative loss of excited Br2(B). Electronic deactivation in collisions of Br2(B) with Ar and He is slow.