Irregular wave tests were conducted in a laboratory flume with an ‘Odessa-type’ bevelled-block submerged breakwater on a sloping bottom. The incident and transmitted waves were subjected to probabilistic and spectral analysis. Although the incident wave heights and periods are described respectively by the Gluhovski and the Rayleigh distributions, for the square of the wave periods, the transmitted heights and periods conform to the Rayleigh distribution irrespective of the depth of submergence of the breakwater. The significant wave heights (Hs) give transmission coefficients comparable to the corresponding monochromatic waves, but theHmax and give 50% higher and upto 28% lower values respectively, the difference increasing with the depth of submergence of the breakwater. The peak frequency of the spectrum does not vary on transmission. Resonant frequencies, where the wave energy is transmitted almost completely, are observed in the process. The resonance occurs at frequencies 1·4, 3·8, 5·6 and 7·0 rad/s, and they remain constant for different submergences of the breakwater. The presence of similar frequencies is also found in the case of monochromatic waves, although the tests are limited. Application of irregular wave tests is recommended in the design of submerged breakwaters.