Polystyrene surfaces have been modified by poly(N-isopropylacrylamide) (PIPAAm) grafting. Beside observing the adhesion and the effect of low-temperature treatment on anchorage-dependent cells, the wetting behavior of PIPAAm-grafted surfaces was studied by dynamic contact angle measurement by Wilhelmy microbalances. Measurements were performed in water at different temperatures and at different speeds of immersion. Contact angle behavior has been explained in terms of heterogeneity of the surfaces, using a slightly modified hysteresis graph. The apparent inversion of advancing and receding contact angles shown at high speeds of immersion has been analyzed in terms of kinetic effect, and it is underlined the lack of a similar critical approach in existing literature data.