With the aim of ascertaining the existance of a correlation between in vivo resistance to Fusarium oxysporum f. sp. dianthi and in vitro response to fungal elicitors and toxic substances, phenylalanine ammonialyase and phytoalexin accumulation, on one hand, and resistance to culture filtrate, on the other, were assayed in "in vitro" cultures of three susceptible and four resistant Dianthus caryophyllus cultivars. Cultivars showing varying degrees of resistance in vivo either tolerated higher culture filtrate concentrations ('Niki') or showed high PAL activity and phytoalexin production when treated with Fusarium elicitor ('Duca'), or responded positively to both treatments ('Mei-Ling', 'Pulcino'). No such responses were shown in tissue cultures of susceptible cultivars. The differential response to the fungal elicitor seemed to be highly specific as genetic differences between cultivars were not observed in tissue cultures treated with other biotic (Phytophthora infestans) and abiotic (HgCl2) elicitors.