CGP-36742 (3-Aminopropyl-n-butyl-phosphinic acid) is one of the first GABAB receptor antagonists that can penetrate the blood-brain barrier after peripheral administration. Although its affinity for GABA B binding sites labeled with a tritiated agonist is modest, being in the low micromolar range, it displays significant pharmacological activity when administered either orally or parenterally. CGP 36742 was effective in the learned helplessness paradigm in rats, dose-dependently improving the escape failures induced by the inescapable shocks, suggesting that it may have an antidepressant profile. CGP36742 displays pronounced cognition enhancing effects in Rhesus monkeys in active and passive avoidance paradigms, in an eight-arm radial maze and a Morris water maze and in a social learning task. CGP36742 blocks the late inhibitory postsynaptic potential and the paired-pulse inhibition of population spikes recorded from CA1 pyramidal neurons of the hippocampus of rats in vitro and in vivo. CGP36742 significantly enhances the release of glutamate, aspartate, glycine and somatostatin in vivo. Chronic administration of CGP36742 causes an up-regulation of GABA(B) receptors in the frontal cortex of rats. The effects of CGP36742 on cognition were investigated in a double-blind, placebo-controlled study undertaken as the first assessment of the efficacy of CGP36742 in 110 patients age 59–85 years with Mild cognitive impairment. The results showed significant improvement in working memory, psychomotor speed and attention with SGS742 as compared with placebo. SGS742 appeared to be safe and well tolerated in this study.