Combination of chemotherapy and surgical resection of metastases is the most promising strategy to improve the fraction of long-term survivors and cured patients in metastatic colorectal cancer. We reproducibly observed evidence of exacerbation of the oxaliplatin-induced neurosensory toxicity following surgery. Total, protein-bound and intra-erythrocytic concentrations of oxaliplatin were measured, whenever possible, immediately prior to surgery and 4, 24 and 48 h following surgical resection. Among 12 patients, seven (58%) patients reported immediate post-operative aggravation of the pre-existing neurotoxicity. At the time of surgery, we detected high intra-erythrocytic platinum concentrations in all patients (median: 1365 micro g/l, range: 820-2968 micro g/l). While ultrafilterable oxaliplatin was not detectable prior to surgery, it could be detected immediately after surgery and during 48 h. These results suggest that patients heavily pretreated with oxaliplatin may experience aggravation of neurotoxicity after surgery, probably through a redistribution of the pool of intra-erythrocytic oxaliplatin biotransformation products into the plasma. This clinical observation might be the consequence of peroperative hemolysis.