Molecular and cellular luminescent biotests were used to reveal the effects of five alkylresorcinol homologues (C7-, C9-, C11-, C12-, and C18-AR) on the thermally induced denaturation and refolding ofbac- terial luciferases, as well as on the synthesis of heat shock proteins. The ARs activities were found to depend on their fine structure and concentration. Direct heat-protective effect of short-chain C7- and C9-AR on the chromatographically pure Photobactrium leiognathii luciferase/oxidoreductase was shown within broad range of concentration (10(-6)-10(-3) M). The long-chain ARs homologues exhibited a similar heat-protective effect at micromolar concentrations only, while their millimolarconcentrations have increased the sensitivity of the model proteins to thermal treatment. The recombinant strain Escherichia coli K12 MG1655 bearing constitutively expressed Vibrio fischieri luxAB genes was used to investigate theARs effect on the intracellular chaperone-independent refolding of bacterial luciferase. The functional activity of heat-inactivated enzyme was restored by micromolar concentrations of short-chain ARs, while long-chain homologues inhibited re- folding in the wide concentration range. The recombinant luminescent E. coli strain bearing the inducible ib- pA'::luxCDABE genetic construction was used to determine the effect of ARs on the synthesis of heat shock proteins (HSP). The preincubation mode of bacterial cells with long-chain alkylresorcinols led to dose-de- pendent stimulation of HSP synthesis (2.7 to 4 times) that confirmed some ARs function as "alarmones". Subsequent thermal treatment resulted in a 5-15-fold decrease of the following HSP induction compared to the control, while the number of viable cells opposite increased 1.5-4-fold. Thus, pretreatment of the bacte- rial cells with long-chain ARs resulted in their preadaptation to subsequent thermally induced stress. Short- chainARs caused less pronounced HSP suppression, although still was accompanied by increased heat resis- tance of the AR-pretreated bacterial cells.