CSF leukemic pleocytosis in the nude rat. CSF samples from both survival and timed histologic studies were used and sampling was performed as follows: Survival study (n = 14): Animals were selected at random for CSF sampling during the observation period and were sampled in groups of three to six animals at 4, 7, 14, 20, and 28 days postinjection. Timed histologic study (n = 27): Three animals each at 1, 2, 4, 7, 11, 14, and 19 days, two animals at 20 days, and seven animals at 21 days postinjection were sampled, followed immediately by death. The total number of CSF samples analyzed is depicted for each time point.