A study of the two-jet mass spectrum measured with the UA 2 calorimeter has revealed a signal from hadronic decays of W and Z bosons above a large background. Production and decay properties of the signal have been measured. The combined production cross-section σ·B(W, Z → two jets) is 9.6±2.3 (stat.)±1.1 (syst.) nb, compared with an expectation of 5.8 nb calculated to order αs 2. A limit on the production cross-section of additional heavy vector bosons decaying into two jets is given as a function of the boson mass.