Most studies of peat hydrology have concentrated on processes below the watertable where pore water pressures and hydraulic conductivity are measured using piezometers. While piezometer head recovery tests in poorly humified bog peats give responses similar to those expected from rigid soils, a number of studies have suggested that matrix compressibility might be important in affecting head recovery test results in well humified bog peats. Until now no data have been available for humified fen peats. We apply the response time theory of Brand and Premchitt (1982) for compressible soils, and Hvorslev (1951) for rigid soils, to head recovery test data obtained from open cylindrical piezometers installed in a humified fen peat in Somerset, England. To the best of our knowledge this is also the first quantitative application of compressible soil theory for piezometers to any peat. Our results show that compression and swelling of the peat matrix do affect the course of head recovery in the piezometers used in the study. We comment on the significance of this finding for the calculation of hydraulic conductivities and pore water pressures in this peat type.