Throughout the history of mankind, many infectious diseases have been treated with plant extracts. Venereal infections are one such group and are regarded as conditions that are highly responsive to traditional treatment. Aqueous, ethanol and ethyl acetate extracts of 13 plants used in South Africa for the treatment of venereal diseases were screened for in vitro antibacterial, antifungal, mutagenic and antimutagenic activities. Antibacterial activity was evaluated using the disc-diffusion and microdilution assays to determine the minimal inhibitory concentration (MIC) values of the extracts. The extracts were tested against the Gram-positive bacteria Bacillus subtilis and Staphylococcus aureus, and the Gram-negative bacteria Escherichia coli and Klebsiella pneumoniae. Among the plants tested, Gunnera perpensa, Harpephyllum caffrum, Hypoxis latifolia and Ledebouria ovatifolia showed the best antibacterial activity. The aqueous rhizome extract of Gunnera perpensa displayed good activity against Gram-negative bacteria with an MIC value of 0.78 mg/ml, and against S. aureus (0.78 mg/ml). Aqueous and ethanol extracts of H. caffrum bark were active against both Gram-positive and Gram-negative bacteria. Hypoxis latifolia aqueous corm extracts exhibited very good MIC values against K. pneumoniae (0.78 mg/ml), E. coli and S. aureus (1.56 mg/ml). Ethanol and ethyl acetate bulb extracts of Ledebouria ovatifolia displayed good activity against Bacillus subtilis bacteria with MIC values of 0.78 mg/ml and 0.39 mg/ml respectively. Antifungal activity was evaluated using the microdilution bioassay. Good activity was shown by the ethanolic bark extracts of Bersama lucens and Harpephyllum caffrum against Candida albicans. Only in the case of Harpephyllum caffrum did aqueous extracts have activity against Candida albicans. In the Ames test, all plant extracts showed a negative genotoxic response except for ethanol and ethyl acetate bulb extracts of Cyrtanthus obliquus which induced mutations in TA98. Moderate antimutagenic activity was observed with the ethyl acetate extract of G. perpensa and the ethanolic extract of H. latifolia. High antibacterial and antifungal activity detected with Harpephyllum caffrum bark extracts resulted in an investigation on seasonal and geographical variation of this inhibitory activity. Seasonal variation in antibacterial and antifungal activities was investigated in order to determine the best collection time to ensure potential high medicinal activity in plant preparations. The highest inhibitory activity was detected with plant material collected in June and December 2003, with a decline in activity when collections were made in September 2004. The chemical profiles of TLC chromatograms were compared and little variation was found, particularly in the case of plant material obtained from the Botanic Garden of the University of KwaZulu-Natal and a 'Muthi' Shop in Pietermaritzburg. Identification of active compounds from G. perpensa and H. caffrum was not successful due to insufficient amounts of isolated fractions. / Thesis (Ph.D.)-University of KwaZulu-Natal, 2006.