The spectroscopic and kinetic characteristics of beta-carotene radical cation (beta-carotene(.+)) were studied by pulse radiolysis in aerated DMSO solution. The buildup of beta-carotene(.+) with k(1) = (4.8 +/- 0.2) x 10(8) dm(3) mol(-1) s(-1) [lambda(max) = 942 nm, epsilon = (1.6 +/- 0.1) x 10(4) dm(3) mol(-1) cm(-1)] results from an electron transfer from beta-carotene to DMSO(.+). The beta-carotene(.+) species decays exclusively by first-order reaction, k = (2.1 +/- 0.1) x 10(3) s(-1), probably by two processes: (1) at low substrate concentration by hydrolysis and (2) at high concentrations also by formation of dimer radical cation (beta-carotene)(2)(.+). Under the experimental conditions, a small additional beta-carotene triplet-state absorption ((3)beta-carotene) in the range of 525 to 660 nm was observed. This triplet absorption is quenched by oxygen (k = 7 x 10(4) s(-1)), resulting in singlet oxygen ((1)O(2)), whose reactions can also lead to additional formation of beta-carotene(.+).