The structure and histochemistry of the poison glands are described in Lycosa tarentula (Lycosidae), four Peucetia species and Oxyopes lineatus (Oxyopidae). All these species show two voluminous poison gland sacs which extend dorsally in the prosoma, over the central nervous system, their base reaching up to the central body of the brain. A muscle layer surrounds the gland sac; it is thicker in Lycosa than in the oxyopids and stops at the beginning of the excretory duct. The latter, rather narrow in Lycosa, starts at the base of the chelicera. It forms a secretory ampulla in the last third of the chelicera, then continues its way for about 400 μm to the entrance of the fang. In oxiopids, the gland sac itself enters the chelicera. An elongated ampulla appears at a quarter (Peucetia) or half (Oxyopes) the length of the cheliceral basal article) and reaches almost the extremity of the chelicera: the excretory duct proper runs only 40 μm before entering the fang. In all cases, the body of the glands presents two distinct regions secreting different substances. In L. tarentula, the main part of the poison gland secretes a complex protein product, with a fine granular appearance; a small accessory lobe, located ventrally in the proximal region of the gland sac, produces a glycoprotein. In oxyopids, the accessory portion of the gland is much more extensive; both regions produce protein; in the ventral proximal pouch, two substances are detected, one of which appears as flat square crystals, isolated inside the cells but stacked up in the gland lumen. The histological characteristics of the poison glands arc examined from a phylogenetic point of view, as well as in relation to the behaviour of these species of hunting spiders.