Abstract: This invention relates to new peptide derivatives of the general formula (I) A-Xaa-Arg-H, wherein A represents a D- or L-isochroman-1-carbonyl, D- or L-isochroman-3-carbonyl group, furthermore an acyl group of the general formula: D- or DL-A'--CH(OH)--CO, wherein A' represents a phenyl, benzyl, 1-naphthyl, 1-naphthylmethyl, 2-naphthyl, 2-naphthylmethyl, 9-fluorenyl, benzhydryl, cyclohexyl, cyclohexylmethyl, 2-pyridyl, 3-pyridyl or 4-pyridyl group, and Xaa represents an L-prolyl or an L-pipecolinic acid residue, and Arg stands for an L-arginine residue, their acid addition salts formed with an organic or inorganic acid and pharmaceutical compositions containing the same. Furthermore the invention relates to a process for preparing them. The compounds of the invention have valuable therapeutic, particularly anticoagulant, properties.