Abstract: In order to assess the antidermatophytic activity and the acute dermal toxicity of Ageratum houstonianum Mill., the essential oil was obtained from the leaves by hydrodistillation and tested against two clinical isolates of dermatophytes: Microsporum gypseum and Trichophyton mentagrophytes. The potentialisation of activity between griseofulvin and the essential oil was evaluated. The proportions of essential oil/griseofulvin tested were 8:2 and 10:1 (w/w). Also, the acute dermal toxicity of this oil was evaluated on guinea-pigs (Cavia porcellus) using a standard method. Agar dilution method with serial dilution of the oil and the mixtures was used for antidermatophytic tests. The percentage inhibition of the fungal growth at each concentration was determined. The MIC of the essential oil was 80 μg mL-1 for the tested dermatophytes. That of the 8:2 mixture was 20 μg mL-1, whereas those of the 10:1 mixture were 8 and 10 μg mL-1 for Microsporum gypseum and Trichophyton mentagrophytes, respectively. Compared to the control group, we noted no diarrhoea, no change in treated skin and on the fur appearance. In the contrary, the degree of sensitivity to noise, reaction to pinch, activity (locomotion) and reactivity decreased with increase in the dose. The LD50 was determined to be 5 g kg-1 b.wt. These data suggest that the essential oil of the leaves of Ageratum houstonianum contains antidermatophytic compound(s) and may not be toxic when used topically. A potentialisation effect was observed between the essential oil and griseofulvin.