Initial evaluation of a new plant life-cycle bioassay for the assessment of the effects of toxic chemicals is presented. The bioassay features a rapid cycling Brassica species that can complete its life cycle in as little as 36 days. The herbicide dalapon (2,2-dichloropropionic acid) was used as the test substance to develop the bioassay. Plants were exposed to nine levels of dalapon solution in a 0.5x geometric series ranging from 0 to 200 ppm (mg/L) in separate postemergence and preemergence application experiments. Harvest biomass was generally reduced by concentrations as low as 12.5 ppm. Similarly, foliar height was reduced at concentrations as low as 25 ppm. Stem diameter was reduced at concentrations above 50 ppm. Although fertile silique counts were quite variable, no siliques were formed at dosages greater than 12.5 and 50 ppm for postemergence and preemergence treatments, respectively. Mortality occurred only with the 200-ppm preemergence treatment. The higher sensitivity of the reproductive stage is of significance to the ecological success of the plant population and demonstrates the value of life-cycle bioassays.