Accurate and reproducible categorization of follicular center cells (FCC) on the basis of their nuclear size and shape is difficult. In addition, the relationship of cleaved to noncleaved FCC has been questioned. For these reasons, 2126 FCC (and 947 mantle cells) from five plastic embedded reactive lymph nodes were studied using a new morphometric approach. Using an image analyzer, the following nuclear features were studied: area (NA); our previously described shape factors which measure ellipticity (NCIe) and irregularity (NCIni); and a new objective measurement of relative chromatin dispersal (chromatin dispersal index, CDI). Definite clefts and nucleoli were visually identified and recorded. Compared to the mantle cells, FCC nuclei were significantly larger, more elliptical, more irregularly shaped, and had more dispersed chromatin. Among the FCC the only correlation that could be identified between the above parameters was that the larger FCC tended to have more dispersed chromatin (r = 0.46). Significantly more dispersed chromatin was, however, associated with nonclefted cells, less irregularly shaped cells having a NCIni less than the median NCIni, cells with nucleoli, and larger cells having a NA greater than the median NA. Clefted FCC had significantly greater nuclear irregularlity compared to nonclefted FCC but a similar degree of ellipticity. Distribution curves for the NA, NCIe, NCIni, and CDI revealed a continuous range of results rather than a limited number of distinct cell types. The addition of an objective quantitative measurement of chromatin dispersal permits a more complete morphometric description of FCC.(ABSTRACT TRUNCATED AT 250 WORDS)