In the quest for alternative treatments against Campylobacter jejuni and Entamoeba histolytica, which are both aetiological agents of diarrhoea world-wide, the in-vitro activities against the two pathogens of extracts of 18 South African medicinal plants have recently been assessed. Forty extracts from the 18 plant species were prepared and tested against 110 clinical isolates of Campylobacter spp. In addition, extracts from eight of the plant species were tested against a standard strain (HM-1:IMSS) of E. histolytica, and the cytotoxicity of each of 19 extracts from 15 of the plant species was explored using Vero cell cultures and microdilution assays. At least one extract of each plant species investigated was found to be active against some of the Campylobacter isolates. Extracts of Lippia javanica and Pterocarpus angolensis had the highest antibacterial activity, each giving a minimum inhibitory concentration (MIC) of 90 microg/ml. Of the extracts tested against E. histolytica, however, only those of P. angolensis and Syzigium cordatum were found to have anti-amoebic activity, with MIC of 1.2 and 7.5 mg/ml, respectively. Although most of the extracts showed little toxicity against Vero cells, with most of the median inhibitory concentrations (IC(50)) recorded exceeding 400 microg/ml, an extract of Bauhinia galpini was quite toxic, with an IC(50) of just 2.7 microg/ml. Acetone and methanol extracts of several of the plants show promise as templates for the design of new anti-diarrhoeal therapies.