A quantitative bioassay utilizing staining of plant cell suspension cultures of Sinapis alba was employed to establish a structure-phytotoxic activity correlation among destruxin B, homodestruxin B, and desmethyldestruxin B, toxins produced by Alternaria brassicae (Berk.) Sacc., the causative agent of Alternaria blackspot of brassicas. In addition, the phytotoxicity of destruxin B, homodestruxin B, and their respective metabolites hydroxydestruxin B and hydroxyhomodestruxin B were tested on resistant and susceptible plant species utilizing in planta leaf assays and leaf uptake of toxin solutions. Overall, the results obtained from punctured leaf and cell staining assays indicated that homodestruxin B (EC(50) 3x10(-4) M) was the most toxic of the five compounds, followed by destruxin B (EC(50) 5x10(-4) M), and desmethyldestruxin B (EC(50)&z.Gt;5x10(-4) M). On the other hand, the hydroxylated destruxins (hydroxydestruxin B EC(50)&z.Gt;5x10(-4) M) were significantly less phytotoxic than the parent toxins.