Technical Abstract: Extracts of both leaves and roots of germinating maize were found to contain endo-beta-1,4-xylanase inhibitors, previously reported only from whole maize meal. The inhibitors seem to be of the xylanase inhibitor protein (XIP) type, since they inhibit endoxylanases of families 10 and 11 and also show some other characteristics similar to XIP inhibitors described in other cereals. Inhibitors from leaves and roots appeared to be similar. Inhibitors extracted in the presence of dithiothreotol (DTT) exhibit a novel thermostability at low pH, with a half-life of more than 10 h at 100 deg C and pH 4.5. However, these inhibitors are less thermostable at higher pH levels. In the absence of DTT, an additional heat-labile but otherwise similar activity also was extracted.