A flash photolysis technique, employing a dye-laser as the flash excitation source, was developed to determine, directly, the rate constant of decay (kd) of singlet oxygen (02' 8) and rate constant of reaction (ktx) between singlet oxygen and 1,3-diphenylisobenzofuran, DPBF, in a variety of solvents. Some results are the following: methanol, kd = (9.0 ± 0.6) X 101 *34 sec-1, k,x = (1.3 ± 0.1) X 109 sec-1 M-1, kdjk,x = 7.2 X 10-5 M; «-butyl alcohol, kd = (5.2 ± 0.8) X 104 sec-1, kIX = (0.80 ± 0.2) X Í09 sec-1 M-1, kdjk,x = 6.5 X 10-6 M; tertbutyl alcohol, kd = (3.0 ± 0.4) X 104sec-1, kTX = (0.57 ± 0.08) 109 sec-1 M-1, kdjktx = 5.3 X 10-6 M. Values in benzene: methanol (4:1), bromobenzene: methanol (4:1), pyridine, dioxane, methanol: water (1:1), methanol: glycol (1 :1), and glycol were also obtained. The resulting ß values (kdlkIX) are in good agreement with ß values determined in other ways. The technique was also shown useful for determination of absolute rate constants of reaction with or quenching of singlet oxygen by compounds such as 2,5-diphenylfuran and MV-dimethylaniline.