Spider venoms are a rich source of neurotoxins, which act on the ion channels, and other chemical receptors of insects and mammals. Phoneutria nigriventer is well known for its aggressive behaviour and is responsible for many accidents in humans, including lethality. On the other hand, only local pain was described in accidents involving Oligoctenus ornatus, another spider from the Ctenidae family. In this work, we made a partial comparison of the toxins from P. nigriventer (PN) and O. ornatus (Oct). Toxicity tests for Oct showed effects such as excitability, salivation, lachrymation, spastic and flaccid paralysis, tail elevation and sometimes death.  Similar symptoms were described previously for PN venom. Determination of the LD₅₀ values for the crude venoms injected ic in mice, revealed that PN female spiders were three times more toxic than the venom from Oct females. Similarly, the venom of PN males was found to be six times more lethal than the Oct males. Additionally, intersexual variations were confirmed for the Oct spiders, with the venom from females being 3,5 times more toxic than the males. The venom components were also fractionated by using a combination of analytical FPLC and HPLC on columns of Vydac C4 and C18 (small pore) respectively. Chromatographic profiles indicate that PN and Oct venoms are complex mixtures. However, some differences can be noticed between these two genera and some peaks appear only in PN. Differences were also observed when the HPLC profiles of the venoms of male and female Oct spider were compared. The purity and molecular mass of each peptide or protein obtained was confirmed by mass spectroscopy, and the N-terminal amino acid sequences of more than 40 were determined by automated protein sequencing. Most of the peptides identified were found to be cationic (pI>7) and with masses in the range 2.6-9.5kDa and most had obvious sequence similarities to the neurotoxins reported from the venoms of Phoneutria spiders. However a new family of small peptides (2.6-3.0 kDa) containing only four cys residues, and exhibiting no sequence homologies with other known peptides from spider venoms was observed.