Two models for meningeal neoplasia have been developed in rats using intrathecal injection of 9L gliosarcoma and Walker 256 carcinosarcoma cells. Tumor cells were injected in unanesthetized animals through an indwelling catheter inserted at the cisterna magna to the level of the lumbar enlargement of the spinal cord. Survival of rats was dependent on the number of tumor cells injected. Spread of tumor was quantified by histology using a grading scale, and functional and behavioral changes were measured. Rats injected with 10(6) 9L gliosarcoma cells showed progressive weight loss, flaccid paralysis, and neurogenic bladder dysfunction and had a median survival of 11 days. The tumor frequently grew as a mass compressing the spinal cord. The 9L gliosarcoma tumor cells markedly invaded the Virchow-Robin spaces but exhibited only minimal invasion of the central nervous system parenchyma. The tumor reached the brain by day 10. Rats injected with 2 X 10(5) Walker 256 carcinosarcoma cells showed progressive weight loss and weakness and had a median survival of 6 days. The tumor grew within the leptomeninges in a discontinuous multifocal fashion and reached the brain by day 4. There was extensive invasion of the central nervous system parenchyma by Walker 256 tumor cells along the Virchow-Robin spaces resulting in hemorrhage and necrosis of grey and white matter. Hot plate and tail flick response times were significantly delayed only in the days immediately preceding death of animals with either 9L or Walker 256 tumor and were not good indicators of tumor progression. Loss of motor coordination and failure of the stepping and placing reflex on the other hand showed good correlation with spread of tumor measured histologically. Control animals injected with 0.9% NaCl or with lethally irradiated tumor cells showed no significant weight loss or functional or behavioral changes. The intrathecal 9L gliosarcoma and Walker 256 carcinosarcoma models show different characteristics of human meningeal carcinomatosis and will be used for studies of experimental chemotherapy with intrathecally administered antitumor drugs.