Integral ESR and time-resolved CIDEP techniques applied to the study of the light-induced yellowing of bleached and unbleached TMP samples provide some further insights into the nature and the mechanisms of the processes. The identity of the phenoxy and ketyl free radical intermediates involved in mese processes is established and the primary triplet photochemical mechanisms of their formation are characterized. The radical scavenging mechanisms responsible for the inhibition of light-induced yellowing in the TMP system by ascorbic acid and triphenylmethyl thiol are formulated.