Abstract: A hybrid plasminogen activator which comprises the five kringle domains of plasminogen linked to the B-chain of t-PA or u-PA via an amino acid sequence comprising, respectively, the t-PA cleavage site between residues 275 and 276 and the cysteine residue 264 of t-PA or the u-PA cleavage site between residues 158 and 159 and the cysteine residue 148 of u-PA, or a derivative of a plasminogen activator comprising the serine protease domain of t-PA or u-PA, in which the catalytic site essential for plasminogen activator activity is blocked by a 2-aminobenzoyl group substituted in the 3- or 4-position with a halogen atom and optionally further substituted with one or more weakly electron-withdrawing or electon-donating groups, wherein the pseudo first order rate constant for hydrolysis of the derivative is in the range 6.0.times.10.sup.-5 to 4.0.times.10.sup.-4 sec.sup.-1 when measured in a buffer system consisting of 0.05M sodium phosphate, 0.1M sodium chloride, 0.

Abstract: A fibrinolytically active hybrid protein which comprises one chain of a 2-chain protease linked to a chain of a different 2-chain protease, or to the same chain of the same protease, at least one of the chains in the hybrid protein being derived from a fibrinolytically active protease, such that the hybrid protein has a catalytic site essential for fibrinolytic activity which is optionally blocked by a removable blocking group.

Abstract: A fibrinolytically active hybrid protein which comprises one chain of a 2-chain protease linked to a chain of a different 2-chain protease, or to the same chain of the same protease, at least one of the chains in the hybrid protein being derived from a fibrinolytically active protease, such that the hybrid protein has a catalytic site essential for fibrinolytic activity which is optionally blocked by a removable blocking group.

Abstract: A hybrid protein which comprises plasmin A-chain linked to urokinase B-chain, the catalytic site of which is blocked by a removable blocking group.

Abstract: A fibrinolytically active hybrid protein which comprises one chain of a 2-chain protease linked to a chain of a different 2-chain protease, or to the same chain of the same protease, at least one of the chains in the hybrid protein being derived from a fibrinolytically active protease, such that the hybrid protein has a catalytic site essential for fibrinolytic activity which is optionally blocked by a removable blocking group.

Abstract: A method for preparing interferon in which MRC-5 cells are induced for 2 to 3 hours with an interferon-inducing medium containing from 0.1 to 50 mg 1.sup.-1 of a ds-RNA, 100 mg 1.sup.-1 of DEAE-Dextran and 250 m.M of sucrose.Other sugars which can be used include glucose, galactose, fructose, mannose and maltose, and a preferred ds-RNA is naturally occurring ds-RNA isolated from P. chrysogenum.