A mechanism of the initiated nonbranched-chain process of form-ing 1,2-alkanediols,carbonyl compounds, and methanolin alco-hol–formaldehyde systems is suggested. The quasi-steady-state treatment is used to obtain kinetic equations that can describe the nonmonotonic (with a maximum) dependences of the formation rates of the products on the concentration of free unsolvated for-maldehyde. The experimental concentrations of the free unsol-vated form of formaldehyde are given at the different temperatures, solvent permittivity, and total concentrations of formaldehyde in water and alcohols. An empirical equation for calculating the free formaldehyde concentration in alcohol–formaldehyde (including water/ethanediol–formaldehyde) systems at various temperatures and total formaldehyde concentrations and an equation for eva-luating solvent concentrations in these systems were derived. The experimental dependence of the ethanediol radiation-chemical yields on formaldehyde concentration in γ-radiolysis of metha-nol–formaldehyde system at 373–473 K is shown.