The present invention relates to novel benzyl(idene)-lactam derivatives, compounds of the formula I ##STR00001## wherein R.sup.1 is a group of the formula G.sup.1 or G.sup.2 depicted below, ##STR00002## wherein R.sup.1, R.sup.3, R.sup.6, R.sup.13 X, a, n and m are as defined herein, their pharmaceutically acceptable salts, and pharmaceutical compositions which include selective antagonists, inverse agonists and partial agonists of serotonin 1 (5-HT.sub.1) receptors, specifically, of one or both of the 5-HT.sub.1A and 5-HT.sub.1B receptors. The compounds of the invention are useful in treating or preventing depression, anxiety, obsessive compulsive disorder (OCD) and other disorders for which a 5-HT.sub.1 agonist or antagonist is indicated and have reduced potential for cardiac side effects, in particular QTc prolongation.