AIM: To explore the relationship between acetylation of histone in total chromatin and p21WAF1 expression regulation in human colorectal carcinoma. METHODS: We analyzed the expression of tumor suppressor gene p21WAF1 mRNA by RT-PCR or realtime PCR in 33 samples of colorectal cancerous tissue, corresponding para-cancerous tissue and normal colorectal mucosa, and also examined the level of acetylated histone H3 in total chromatin using Western blotting. RESULTS: The expression level of p21WAF1 mRNA was significantly lower in colorectal cancerous tissue from 33 patients than in para-cancerous tissue and normal colorectal mucosa (2377.95±865.80 vs 3216.58±1149.42 and 3541.61±1433.17 respectively, P < 0.01). In addition, when p21WAF1 mRNA expression was undectectable or at very low level (50% less than that in adjacent tissue and normal colorectal mucosa) in all tissues, the level of acetylated histone H3 in colorectal cancerous tissue was significantly lower than that in corresponding para-cancerous tissue and normal colorectal mucosa in five of seven (71.43%) cases. The transcriptional level of p21WAF1 in colorectal carcinoma might not be associated with its biological behaviors. conclusion: The down-regulation of p21WAF1 transcription is involved in the tumorigenesis and development of colorectal carcinoma. The downexpression of p21WAF1 mRNA in colorectal carcinoma might be associated with histone hypoacetylation in chromatin but not with biological behaviors. AIM: To explore the relationship between acetylation of histone in total chromatin and p21WAF1 expression regulation in human colorectal carcinoma. METHODS: We analyzed the expression of tumor suppressor gene p21WAF1 mRNA by RT-PCR or realtime PCR in 33 samples of colorectal cancerous tissue, RESULTS: The expression level of p21WAF1 mRNA was significantly lower in colorectal cancerous tissue from 33 patients than in para-cancerous tissue and Normal colorectal mucosa (2377.95 ± 865.80 vs 3216.58 ± 1149.42 and 3541.61 ± 1433.17 respectively, P <0.01). In addition, when p21WAF1 mRNA expression was undectectable or at very low level (50% less than that in adjacent tissues and normal colorectal mucosa) in all tissues, the level of acetylated histone H3 in colorectal cancerous tissue was significantly lower than that in corresponding p The transcriptional level of p21WAF1 in colorectal carcinoma might not be associated with its biological behaviors. conclusion: The down-regulation of p21WAF1 transcription is involved in the tumorigenesis and development of colorectal carcinoma. The downexpression of p21WAF1 mRNA in colorectal carcinoma might be associated with histone hypoacetylation in chromatin but not with biological behaviors.