The intrinsic viscosity ([η]) in water of a sample of linear poly( N-methylol acrylamide) (PMAM) has been measured over the range 278–348 K and the swelling ratio ( Q) in water of a sample of chemically crosslinked PMAM has been determined within the interval 278–353 K. The plots of [η] and Q versus temperature ( T) both exhibited a maximum. The viscometric behaviour is consistent with an analysis based on excluded volume theory, which indicates the existence of a critical solution temperature both below (263 K) and above (375 K) the maximum. The swelling data were analysed on the basis of the Flory-Rehner theory which yielded a predicted minimum in the dependence of the polymer-water interaction parameter (χ) with T, thus according with the observed maximum in Q versus T. Prolonged heating of linear PMAM and its xerogel yielded products, which were no longer soluble or swellable, respectively, in water. The induced crosslinking proposed as the cause has been confirmed by chemical and infra-red analysis.