In culture, pectic enzymes were produced constitutively by Verticillium albo-atrum Reinke et Berthold; pectin and polypectate stimulated their secretion. Levels of endo-polygalacturonase (PG) and exo-pectin lyase (PL) were high, but only small amounts of pectin methyl esterase (PME) were detected. As reported earlier, cellulase (C x) was inducible, being formed only in the presence of cellobiose or cellulose in the medium. Several PL components were detected in infected lucerne ( Medicago sativa L.), and were similar to those produced in culture by the fungus. High concentrations of PL coincided with the onset of wilting, suggesting that this enzyme may be involved in the processes leading to gel blockage of xylem vessels. A further unidentified protein component of mol. wt. 40000 promoted a marked increase in the viscosity of a 0·5% pectin solution at pH8·5, and could be important in catalysing gel formation. Neither PG nor C x could be implicated in wilting since they were detectable only after advanced symptoms had developed.