The presence of apoptotic bodies and of intraepithelial lymphocytes (IELs) were assessed in colorectal adenomas and adenocarcinomas induced in 158 rats by two different carcinogens: 1,2 dimethylhydrazine (DMH) and glutamic acid pyrolysate (GLU-P-1 and 2). Apoptotic granules were present in 97.5% (n=40) of the 41 GLU-induced adenomas and adenocarcinomas, but only in 20.5% (n=24) of the 117 DMH-induced tumours. IELs were found in 95.1% (n=39) of the 41 GLU-induced tumours but only in 21.4% (n=25) of the 117 DMH-induced neoplasias. The differences were significant (p< 0.001). The presence of IELs and apoptotic granules in GLU tumours (and their absence in the majority of the DMH tumours) is new evidence that IELs are the cells from which many of the apoptotic granules--seen in colorectal neoplasias--derive. GLU neoplasias were induced following daily treatment, for 24 months (about half the life span of the animals) and DMH neoplasias by weekly doses, for a period of only 2.8-6 months. It would appear that 'slowly growing' colorectal GLU neoplasias often attract IELs and trigger lymphocytic apoptosis whereas 'quickly growing' DMH tumours seldom evoke those reactions.