The objectives of this study were to determine the efficacy, range of activity and effective concentrations (EC50 and EC80) of abamectin as a seed treatment of tomato against Meloidogyne incognita, M. arenaria and M. javanica. The study revealed that abamectin seed treatment at concentrations ranging between 0.3 and 1 mg a.s. seed−1 is highly effective against the three species of root-knot nematodes, retaining its efficacy in the soil for 8 weeks. The highest EC50 found was reached at 0.2 mg a.s. seed−1. The highest EC80 for the number of egg masses per g root in the three Meloidogyne species was attained at 0.51 mg a.s. seed−1. Abamectin as a seed treatment is promising for the control of root-knot nematodes in the field since only low amounts of active ingredient are required to give adequate protection in the most sensitive stages of tomato root growth and development.