Latex of dandelion roots contains a serine proteinase that hydrolyzes a chromogenic peptide substrate Glp-Ala-Ala-Leu-pNA optimally at pH 8.0. Maximal activity of the proteinase in the roots is attained in April, at the beginning of plant development after the winter period. The protease was isolated by ammonium sulfate precipitation of the root extract followed by affinity chromatography on a Sepharose-Ala-Ala-Leu-mrp and gel filtration on Superose 6R performed in FPLC regime. Pure serine proteinase named taraxalisin was inactivated by specific inhibitors of serine proteinases, diisopropylfluorophosphate (DFP) and phenylmethylsulfonylfluoride (PMSF). Its molecular mass is 67 kDa and pI 4.5. pH stability range is 6-9 in the presence of 2 mM Ca2+, temperature optimum is at 40 degrees C; Km=0.37+/-0.06 mM. The substrate specificity of taraxalisin towards synthetic peptides and insulin B-chain is comparable with that of two other subtilisin-like serine proteinases, cucumisin and macluralisin. The taraxalisin N-terminal sequence traced for 15 residues revealed 40% coinciding residues when aligned with that of subtilisin Carlsberg.