The relationship between the initial (P-i) and final (P-f) population densities of Meloidogyne javanica and yield of watermelon, Citrullus lanatus, cv. Sugar Baby were determined in pot and field experiments. In the pots, the maximum reproduction rate of the nematode was 14, and the equilibrium density was 49400 eggs/100cm(3) of soil. Yield data represented as fresh top weight fitted the Seinhorst damage function (P<0.001, R-2=0.7), and the minimum relative yield (m) was 0.65 at P(i)3200 eggs/100cm(3) of soil and the tolerance limit (T) 74 eggs/100cm(3). In the field experiments (2011 and 2012), the maximum reproduction rate was 73 and 70, and the equilibrium density 32 and 35 second-stage juveniles (J2)/100cm(3) soil. Yield data represented as fruit weight fitted the Seinhorst damage function in 2011 (P<0.001, R-2=0.92) and the m- and T-values were 0.63 and 20 J2/100cm(3) of soil, respectively. Meloidogyne incognita and M. javanica needed similar length of time for development to egg-laying females and life cycle completion at 24.4 degrees C.