Polyamine levels (putrescine, spermidine and spermine) in colorectal cancers (n = 25) were measured in order to assess their importance as markers of cellular proliferation. Colonic mucosa from healthy resection margins of patients with diverticular disease (n = 5) was used as control material. Polyamine levels (expressed as nanomoles per 100 mg tumour) in cancers ranged from 0.8 to 7.9 for putrescine (mean: 2.3 +/- 0.7), from 6.5 to 22.8 for spermidine (mean: 13.9 +/- 0.9) and from 13.0 to 37.5 for spermine (mean: 22.1 +/- 1.3). Mean spermidine and spermine content of cancers was more than three times mean spermidine (3.92 +/- 0.8), and more than four times mean spermine (5.0 +/- 1.2), content of normal colonic mucosa (P less than 0.01). Polyamine content of colorectal cancers was independent of tumour site, Dukes' stage, histological grade and the presence of palpable liver metastases at laparotomy. Because colorectal cancers contain such high levels of spermidine and spermine, polyamines may play an essential role in the regulation of their growth.