In balanced experiments with rats the influence of the period of adaptation on nutrient digestibility in diets containing cellulose (CEL), guar gum (GG), pectin (PEC) or retrograded high amylose maize starch (RS) was studied. Inclusion level was 80 g/kg diet DM except for the retrograded high-amylose maize starch, where the level was 316 g/kg diet DM. A diet containing normal maize starch only acted as a controi diet (FF). The apparent digestibilities of DM, NSP, starch and protein were determined after adaptation periods of 4 d and 2, 4, 6 and 8 weeks. The digestibility of nutrients was affected by diet (P < 0.001) as well as by the period of adaptation (P < 0.001). The digestibilities of DM, NSP and starch increased asymptotically during the course of the experiment. The asymptotic progress over time was most pronounced for the GG, PEC and RS diets. The estimated periods of adaptation required for stable DM digestibility were approximately 1 week for the GG, PEC and RS diets and < 4 d for the FF and CEL diets. The digestibility of NSP in the GG and PEC diets was also stable after approximately 1 week, while it was stable from < 4 d for the CEL diet. However, PEC increased the faecal content of uronic acids for at least 2 weeks. A stable starch digestibility required 1 month in the case of RS and 3–10 d for the other diets. The high faecal content of glucose for the RS diet decreased during all 8 weeks but was still high at the close of the experiment. The apparent protein digestibility changed over time in a parabolic rather than an asymptotic fashion. The GG, PEC and RS diets increased the amount of N excreted by the faecal route.