To study the expression of tissue carcinoembryonic antigen (CEA) by immunoperoxidase staining in colorectal adenocarcinomas and its relation with preoperative serum CEA and clinicopathological parameters, we studied 85 unselected patients who underwent resective surgery for colorectal adenocarcinomas and were followed up for a mean of 66 mths. All tumors except 2 showed positive staining for CEA. The staining pattern was classifiable into 4 types: apical, cytoplasmic, basolateral and stromal, according to the predominant sites of staining. We found a significant positive correlation between tissue CEA staining pattern and preoperative plasma CEA. Plasma CEA levels were higher when tumor cell staining extended to basolateral regions of the cells and into stromal tissues rather than restricted to apical and cytoplasmic regions (p = 0.012). Furthermore, tissue CEA staining also correlated positively with vascular invasion by tumor cells (p = 0.046), with basolateral and stromal types associated with more frequent vascular invasion than apical and cytoplasmic types. This was in contrast to the preoperative CEA which did not correlate with vascular permeation. We speculate that tissue CEA staining is useful in indicating possible vascular invasion even at early stage whereas vascular invasion by a larger tumor bulk or even tumor metastases may be necessary to produce an increased plasma CEA level that is detectable. On the other hand, preoperative plasma CEA had a strong, positive relationship with tumor stage and mortality (p < 0.001 for both). Preoperative CEA was higher in tumors showing moderate and poor differentiation, although it did not reach statistical significance (p = 0.068), whereas tissue CEA staining had no correlation with tumor differention.(ABSTRACT TRUNCATED AT 250 WORDS)