M.Tech. (Biomedical Technology) / A study was conducted with the aim to determine the incidence and contamination levels of fumonisin (FB) and FB producers in South African compound feeds. A total of 90 compound feed samples were screened for FB producing Fusarium species conventionally based on the morphological macroscopic and microscopic features. Data revealed that Fusarium spp. were most prevalent in feeds for chicken with an incidence rate of 34% recorded followed by cattle (6%) and pig feed (1%), meanwhile no Fusarium spp. was recovered from any of the horse feed analyzed. Similar samples were also analyzed for FB and in general, data indicate that 68% of samples were positive for FB1 which was the most frequent, ranging from 24 to 5515 μg/kg (mean concentration: 796.5 μg/kg). Quantification of fum 1 gene in 30 animal feed samples was performed by quantitative real time-polymerase chain reaction (qRT-PCR). Detection as well as quantification of fum 1 gene in animal feed was made possible but a positive correlation between fum 1 gene and FB levels was not established, however, an association between fungal contamination, FB and the determined fum 1 gene concentrations was evident in this study. The cytotoxic effect of FB extract from feeds was evaluated in vitro on human lymphocyte cells. Data obtained revealed that cell viability of lymphocytes was strongly influenced by both the concentration of toxin and duration of exposure. This study demonstrates that in South Africa, animals are constantly exposed to FB via consumption of feeds contaminated with the toxin even though the levels obtained are within the acceptable levels. Their presence thus highlights the need for proper quality control measures to be put in place at every step in the animal feed production chain.