Golgi-prepared cerebella from 1, 10, 13 and 30-day-old kittens were analyzed and compared with 30-45 days in vitro (DIV) HRP-stained organotypic cultures of newborn kitten cerebella. Computer reconstructions and morphometric parameters allowed a quantitative analysis of the Purkinje cell (P-cell) dendritic trees. In intact animals the dendritic organization appeared monoplanar as early as one day after birth and biplanar in 85% of the cells at day 13; however, by day 30, 90% of the cells were monoplanar. During the first 4 postnatal weeks, the dendritic expansion was due mostly to an increase in the total number of segments and the total dendritic length, whereas the overall mean segment length remained almost unchanged. In culture, the 30-45 DIV P-cell dendritic trees always appeared reduced in size when compared to their in vivo counterparts due mostly to a reduction in the total number of segments. Nevertheless, these cells retained several primary dendritic trunks and their overall mean segment length was longer. These supposedly 'mature' cultured P-cells never reached full adult development: a discriminant analysis classified them as resembling those from intact animals of 13 days but often maintaining some properties of newborn animals. These results demonstrate that the presence of all normal inputs is required to achieve the full elaboration and the planar disposition of the P-cell dendrites.