The integrated absorption of the b1 - X transition of the Me radical (2160 .ANG.) and the B - X transition of the allyl radical (2100-2400 .ANG.) were compared, in the flash photolysis of 1-butene. From the f value of the Me band, the oscillator strength of the allyl transition was recorded as 0.140 (+-0.028). The rate coeff. for recombination of allyl radicals was in the range 8.5(+-3) * 1012 cm3 mole-1 sec-1.