A Ki-67 index was determined in 63 fine needle aspiration cytology (FNAC) specimens from patients with rectal cancer, 21 with primary cancers and 42 with local recurrences. Seventeen of the patients had received external irradiation before the examination. In primary cancers, in recurrences as well as in the post-irradiation cases, the mean percentage of Ki-67 positive cells was about 55% with a wide variation. The percentage of Ki-67 positive cells was independent of the length of the recurrence-free period. In conclusion, the Ki-67 antigen may well be studied in FNAC specimens. The presence of antigen did not correlate with development of recurrence, length of recurrence-free period or irradiation prior to the analysis.