AbstractIncremental theory of plasticity has been used to derive associated and non‐associated stress–strain relations for analysing the undrained stress‐strain response of isotropic normally and lightly overconsolidated clays. A series of comparisons between the theoretical stress‐strain‐pore pressure response and laboratory test results for 3 in. × 6 in. samples of very high degree of repeatability and reproduceability have been described. From these comparisons it can be seen that both the associated and, non‐associated Cam clay models appear to give consistently the best correlations between the theoretical results and the experimental