AbstractNon‐linear interactions between solvent and solute are observed in the radiolysis of binary organic mixtures. The use of labelled molecules to diagnose both the nature of the excited solvent species and also the nature of the interaction between these excited secties and the solute molecules will be described.The particular systems discussed in detail will be: 1. cyclohexane +14C‐benzene; 2. tritiated cyclohexane +14C‐benzene; 3. tritiated cyclohexane + benzoquinone; 4. tritiated cyclohexane + cyclopentene; 5. cyclohexane +14C‐cyclohexene; 6. cyclohexane or cyclohexane d12+ benzene or benzene‐d6; 7. cyclohexane‐d12+ cyclopentane; 8. various mixture of cyclohexane, cyclopentane and deuterated analogs with corresponding olefins and the deuterated olefins; 9. mixtures of light and heavy water vapor with cyclopentane, methane, cyclohexane and other hydrocarbons.Analysis of the products obtained in the irradiation of these systems has been informative about the nature of the quenching and scavenging processes wich take place and also about the nature of the, reactive speci