The significance of the carnivorous habit of Pinguicula vulgaris L. was studied when plants were fed with insects and/or supplied with complete nutrient solution in the substrate. In most cases, plants supplied with insects alone or in combination with fertilizer showed higher values for dry wt, number and length of leaves, and concentrations of nitrogen and phosphorus. The amount of nitrogen absorbed when insects were added to fertilized plants was larger than the insects contained. It is inferred that P. vulgaris uses both nitrogen and phosphorus from the insect. It is hypothetized that some other substance is also obtained from the insects and used for the uptake by roots or utilization of nitrogen. No major differences in response were found between plants from the two sites studied, i.e. one relatively rich and one relatively poor mire in the Torneträsk area, North Sweden.