The major compound responsible for toxicity toArtemia salinaof someFusarium tricinctumstrains has been isolated, and its structure has been elucidated by spectroscopical methods, i.e. UV, IR, MS,1H‐NMR and13C‐NMR. The novel compound, trivially named visoltricin, is the first imidazole derivative produced byFusariumspp., and its structure has been established as the methyl ester of 3‐[l‐methyl‐4‐(3‐methyl‐2‐butenyl)‐imidazol‐5yl]‐2‐propenoic acid (molecular formula C13H18N2O2; MW = 234.297). Visoltricin was toxic toA. salinalarvae (LD50= 8.5 × 10‐7M), and inhibited the growth of six human tumour cell lines (out of 60 lines tested) at concentrations lower than10–5M. Tested on rabbit eye it showed an interesting miotic activity similar to that of pilocarpine, a miotic agent largely used in the therapy of glaucoma. This biological activity could be explained in part by the anticholinesterase properties shown by visoltricin towards both human serum and pure enzymes (EC 3.1.1.7 and EC 3.1.1.8). Kinetics studies showed for visoltricin a mixed‐type and reversible inhibition of the EC 3.1.1.7 enzyme with the competitive inhibition constant (Ki) = l.9×10−4M.