The present work examined some central nervous actions of prostaglandin Dz (PGD2), which is the most prevalent prostaglandin in rodent brain. The effects of PGD2 were compared with those of PGE z and PGF2~. The prostaglandins were administered intracerebroventricularly (ICV) to conscious rats using the method of Herman (1970). All three prostaglandins studied produced depressive behavioral effects, causing obvious sedation at doses of 2.0 lag and 20.0lag ICV. PGD2 and PGE z significantly reduced spontaneous motor activity at doses of 2.0 lag and 20.0 lag ICV. PGF2~ was less effective; only 20.0lag significantly inhibited motor activity. At a dose of 20.0 lag ICV all three compounds were shown to block convulsions induced by pentylenetetrazol. PGD2, the most effective prostaglandin in this respect, was still slightly anticonvulsive at a dose of 2.0 gg ICV. PGF2~ hat the weakest anticonvulsive potency. PGE2 and PGF2~ (2.0lag and 20.0lag ICV) caused a marked hypertensive effect, whereas PGD2 at the same dose levels only produced a small increase in blood pressure. PGE2 and PGF~ (2.0lag and 20.0lag) also exerted marked pyrogenic actions. The effects of PGD2 on body temperature were variable. When given at a dose of 20.0 lag ICV, it caused slight hyperthermia whereas a lower dose (2.0 lag ICV) induced a moderate fall in body temperature. These findings suggest a relationship between the actions of the different prostaglandins on blood pressure and body temperature.