Ether lipid 1-O-octadecyl-2-O-methoxy-rac-glicero-3-phosphocholine (ET-18-OCH3) is an immunomodulator with antineoplastic activity. Its analog compounds PAF and CPAF share some of its biological effects. In our experiments, even very small amounts of ET-18-OCH3 released a remarkable quantity of nitric oxide (NO) from rat astrocytes cultured in vitro. The NO biosynthesis was inhibited by pretreatment with the antagonist BN 50730. The effect of ET-18-OCH3 was greater than that of the LPS inducer. PAF did not produce NO, even at high doses, while the nonmetabolizable CPAF only induced a significant release of NO from 12 micrograms/ml onwards. These results demonstrate that ET-18-OCH3 is functionally active also in astrocyte cultures. Stimulation of NO biosynthesis is of a great value on account of its the known effect as a neurotransmitter, potentiator of immune defences and possible modulator of cerebral circulation.