Lymph node metastases are an important determinant of prognosis following surgery for colorectal cancer. A xylene alcohol clearance technique has been employed in Guildford to facilitate the identification of lymph nodes in the mesorectum of rectal cancer specimens. The numbers of lymph nodes and lymph node metastases were compared with seven other centres and St. Mark's Hospital, where clearance techniques were not employed in patients undergoing a randomized trial of pre-operative radiotherapy for rectal cancer. The total number of lymph nodes identified per patient in the mesorectum of patients at Guildford (mean = 23.1 +/- 1.18) was significantly higher when compared with patients at St. Mark's Hospital alone (mean = 13.1 +/- 0.86) and the seven combined "non-cleared' centres (mean = 10.5 +/- 0.6) (P less than 0.001). The number of lymph node metastases per patient was significantly higher in the Guildford series (mean = 3.21 +/- 0.58) when compared with the seven combined centres (mean = 1.9 +/- 0.3) (P less than 0.05). The numbers of lymph node metastases found in the lowest part of the specimen close to the levator ani were significantly higher in the Guildford patients (mean = 1.2 +/- 0.4) compared with St. Mark's Hospital (mean = 0.13 +/- 0.1) and the seven combined 'non-cleared' centres (mean = 0.56 +/- 0.1). This clearance technique identified not only a greater number of lymph nodes but also more metastases within those nodes, particularly in the supralevator area of the mesorectum.