Experiments were carried out to study the effect on the degree of crosslinking of: (a) short term (1 or 5 min) high (50 degrees C) temperature glutaraldehyde (GA) fixation of native collagen membrane, (b) a combination of GA presoaking at low temperature [0 degree C or room temperature (rt)] followed by short time (< 3 min) heating of synthetic collagen fleece in a multilayer diffusion model. As a measure for the degree of crosslinking the shrinkage temperature (Ts) was determined. Short time (1 or 5 min) high temperature (50 degrees C) fixation using 0.1% GA solution caused the shrinkage temperature to increase to 80% and 93% respectively, of the maximum attainable Ts employing GA crosslinking (ca 91 degrees C). Fixation with 0.01% GA for 5 min at 50 degrees C appeared equally as effective as 1 min with 0.1% GA. Although an elevated fixation temperature (from rt to 45 degrees C) was found to produce a substantial increase in Ts of the collagen sheets, a homogeneous distribution of cross links was not obtained by this method. Presoaking the samples at rt (1 h) or at 0 degree C (3 h) with subsequent short time heating to 45 degrees C caused an almost equal rise in shrinkage temperature in Ts throughout the collagen samples.