We have analyzed the loss of heterozygosity (LOH) of TP53 in a series of 96 sporadic colorectal carcinomas by means of PCR, using two microsatellite sequences (TP53 and Mfd152), to investigate its possible relationship with several clinicopathological variables in the Spanish population. Forty six of the 96 patients (48%) showed loss of one allele of the microsatellite TP53, Mfd152 or both, when compared with normal colorectal mucosae and blood samples of the same patient. This high percentage of LOH seems to corroborate the important role of p53 in sporadic colorectal cancer. However, we have found that LOH on this region is independent of histological grade and tumour location. With regard to tumour Dukes' stage, the fact that a substantial proportion of tumours show LOH on 17p from the first stages of the disease could imply that this alteration is not related with the invasiveness acquisition staging.