A series of 1-isoquinolinylguanidines are shown to be potent inhibitors of uPA with selectivity over tPA and plasmin. Potency is enhanced by the presence of a 4-halo and a 7- aryl substituent, particularly when substituted by a 3-carboxylic acid group. Compound 13j (UK-356,202) combines excellent potency and selectivity, and has been selected as a candidate for clinical evaluation.