Rumen degradability of fresh (61% DM - end of wax-ripe stage), freeze dried, and oven dried (at 40°C for 5 d and 60°C for 1 and 3 d) maize grain was determined by in situ incubation for 0, 2, 4, 8, 12, 16, 24 and 48 h with four nonlactating Holstein-Friesian cows. Oven dried material was degraded at a lower level compared to fresh and freeze dried material. The degradability values of organic matter, starch and crude protein of fresh and freeze dried grains differed significantly from oven dried grains until an incubation time of 12 h (P<0.01). Correlation coefficients between organic matter and starch degradability, organic matter and crude protein degradability and starch and crude protein degradability were 0.99, 0.97 and 0.97, respectively. In the early hours of incubation the fresh material showed a higher degradability (washing losses up to 19 percentage points) compared to the freeze dried material. Above 8 h of incubation the freeze dried material showed slightly higher degradability values. Effective degradability decreased with increasing temperature, especially at high outflow rates. It can be concluded that it is essential to pay attention to sample preparation, which has to be described for comparing results from different degradability studies. Besides, the results show that oven drying increases the bypass of starch.