The amounts of eight putative neurotransmitters or modulators (acetylcholine, dopamine, noradrenaline, adrenaline, GABA, taurine, glutamic acid, glycine) were determined from the CNS of 12 species of five different spider families (Theraphosidae, Agelenidae, Araneidae, Lycosidae, Salticidae). Comparatively high contents of acetylcholine and noradrenaline could be found in the CNS of hunting spiders, higher contents of GABA and taurine were visible in the web-building spider families, while extraordinarily high amounts of glutamic acid were confined to the Theraphosidae. The results obtained are compared with findings from other arthropod groups and the role of putative transmitters or modulators in the spider CNS is discussed in relation to behavioural differences within the families investigated.