It is shown that paraazoxyanisole has four solid-crystal forms. The heats and temperatures of melting and transition are related by the following five equations: Qm(IV) = Qm(II); Qm(IV) = Qm(I) + Qm(III); Tm(IV) = Tm(III); Ttr(II-III) = Tm(I); and Qtr(II-III) = Qm(I), Qm(SCIV) = 52.0 ± 0.3 kJ/mol. Earlier, similar relationships were established for the third homologue of paraazoxyanisole, Qm[SCIV(C3)] = 48.2 kJ/mol. It is found that for paraazoxyphenetole, Qm[SCIV(C2)] = 46.0 kJ/mol. © 2002 MAIK "Nauka/Interperiodica".