Reaction of hydrogen atoms and pyrene in liquid methanol was studied via the hydrogen addition product, i.e., the pyrene radical, by nanosecond transient absorption spectroscopy, The rate constant for hydrogen addition is measured to be 7.2 x 10(9) M(-1) s(-1) in methanol, and that of hydrogen abstraction from methanol is 2.0 x 10(8) s(-1). Oxygen is shown to react with the pyrene radical with a slower than diffusion-controlled rate 1.4 x 10(8) M(-1) s(-1). The G value of hydrogen atom formation from molecular dissociation in radiolysis of liquid methanol is measured as 1.5 per 100 eV.