In a series of investigations to find out new biologically active fungal metabolites, we recently discovered that the ethyl acetate extract of a teleomorphic fungus, Hamigera avellanea Stolk et Samson, is lethally toxic to mice. Repeated chromatographic separations of the extract on silica gel columns were tested for toxicity to mice, affording two new compounds named avellanins A and B. The avellanins led to the death of mice and rats after a great increase in blood pressure. Avellanins A and B are two new fungal metabolites with pressor effect isolated from Hamigera avellanea, and their structures were found to be cyclo-(N-methyl-D-phenylalanyl-D-alanyl-L-isoleucyl-2-aminobenzoyl-L-prolyl) and cyclo-(N-methylphenylalanyl-alanylvalyl-2-aminobenzoyl-prolyl), respectively.