Proliferative activity in 106 cases of non-Hodgkin’s lymphoma was estimated using the monoclonal antibody Ki67 and by counting the number of mitotic figures. The percentage of Ki67-positive cells was compared with the median number of mitotic figures per square millimeter. Both Ki67 positivity and the number of mitotic figures were found to be greater in high grade than in low grade lymphomas

although there was an overlap between the two grades of malignancy. A close correlation was found between the number of mitotic figures and the percentage of Ki67-positive cells not only in all lymphoma typo taken together （r

s

= 0. 834 . P

<

0. 001）. but also in B-cell lymphoma （r

s

= 0. 8 1 P

<

0. 001） and T-cell lymphoma （r

s

= 0. 764. P

<

0. 00 1） taken seprately. Thus

both methods are useful for the estimation of proliferative activity. but each method has its advantages and disadvantages.