Quaternary ammonium lipids containing long hydrocarbon-chains can cause deleterious effects when administered to many types of microorganisms. Some compounds have potent activity against spermatozoa and the HIV virus. Consequently, quaternary ammonium lipids are key components in spermicidal and antiseptic formulations. Surface-active quaternary ammonium lipids, containing a hydrophobic and hydrophilic moiety, will aggregate into micelles when dissolved in water above a narrow concentration range, termed the critical micelle concentration (CMC). This project investigates how the CMC relates to spermicidal and microbicidal properties. The CMC’s of the AD-nX and AT-nX compounds [see documents for figures] were determined by conductivity measurements. Relationships among the CMC and factors such as alkyl-chain length, head-group size, counteranion, and biological activity are discussed. [See document for figures of ADn and ATn] / Master of Science