Quaffing a potion of gain ability can increase your attributes. Quaffing a cursed one does nothing, nor does quaffing a noncursed one while wearing a ring of sustain ability; in either case, the potion will not be identified. Blessed increases all your attributes, uncursed increases just one at random. Attributes will be increased by one point. Note that only 6 tries will be made to find an attribute which isn't already at its maximum. If all six fail, you will get the usual stat-maxed message for the last one picked: "You're already as [strong, wise, etc.] as you can get!"