The research presented here was conducted in order to determine the influence of exogenous traumatic acid (TA) on the growth, metabolism, and antioxidative activity of vascular water plant, Wolffia arrhiza Wimm. The research was concerned with TA influences, in concentrations of 10^-8 M – 10^-4 M, on fresh W. arrhiza, and on primary metabolites, such as monosaccharides, proteins, chlorophylls a and b, and carotenoids. It was determined that TA causes a substantial increase in these metabolites compared to the control, especially at concentrations of 10^-7 – 10^-6 M. Polyacrylamide gel electrophoresis of proteins (SDS-PAGE) was conducted in order to specify in more detail the qualitative changes in proteins, whose synthesis is stimulated by TA. Under the influence of TA W. arrhiza cells saw an induction of de novo synthesis of 3 proteins with molecular weights of 10, 58, and 90 kDa. It was proven that 10^-7 – 10^-6 M concentrations of TA also increase photosynthesis intensity and the activity of antioxidative enzymes (ascorbate peroxidase, catalase, glutathione reductase, and superoxide dismutase). In cells treated with exogenous TA, lipids' peroxidation decreases (expressed as a drop in malonyl dialdehyde) and sulfhydryl (SH) groups in proteins increase. Based on our research, TA plays an important role in the regulation of growth and metabolism in W. arrhiza. Our results also show that TA possibly participates in the activation of antioxidant enzymes and its probable participation in the metabolic responses of lower water plants to oxidative stresses.