The effects of exposure to moisture on the mechanical properties of a series of adhesively-bonded structures are reported. Changes observed in the maximum load, shear modulus, strain at maximum load, fracture energy, fracture toughness and stress are discussed and correlated with variation of the dielectric parameters. An initial increase in fracture toughness observed in the joints correlates well with the uptake of moisture having led to a lowering of the glass-rubber transition temperature. Differences in the ultimate strength and energy to failure for different surface pretreatments are observed. Loss in mechanical properties observed over the period of the study are paralleled by changes in the dielectric properties of the joints.