Accidents involving venomous animals have always caught the attention of mankind due to their lethality and other clinical implications. However, since the molecules obtained from animal venoms have been the product of millions of years of evolutionary process, toxins could be used to probe physiological mechanisms and could serve as leads for drug development. The present work reviews the state of the art pertaining to venom molecules from Brazilian medically important arachnid species bearing potential biotechnological applications. Special focus is given to toxins isolated from the scorpion Tityus serrulatus and the spiders Phoneutria nigriventer and Lycosa erythrognatha, whose venoms possess molecules acting as erectile function modulators and as antihypertensive, analgesic, neuroprotective and antimicrobial agents.