Digestibility in vitro (by 0.02% trypsin plus chymotrypsin) of the samples as determined by reaction with o-phthaldialdehyde (OPA) showed that there was no significant difference between the heated Na caseinates and the control, although there was a trend for the digestibility of the sample heated at 140°C for 30 min to be somewhat lower than that of the others after incubation for 2 h. However, the differences in digestibility between the control and heated samples (120 and 132°C for 60 min) became greater when the level of enzymes used was increased to 0.08%.