Abstract Aquatic animals subjected to osmotic stress may show an increased toxicity response to water contaminants. Artemia salina cysts were hatched and raised in 50% or 25% artificial seawater at 19°C and the resulting Stage II nauplii were exposed to various organic chemicals to determine immobilisation concentrations (IC 50.24h). Simple linear regressions were used to compare the IC 50 values at both salinities to n-octanaol/water partition coefficients. The fundamental equation is described by log 1/C 50 = a + b × log P. Positive linear regressions were observed at both salinities indicating a nonspecific-type toxicity. The regression and correlation parameters were not significantly different between the two relationships. As the salinity was decreased, however, the intercepts increased and the slopes decreased in a slight but consistent fashion. The present quantitative model appears to be relatively insensitive to changes in the toxicity of organic chemicals to osmotically stressed A. salina nauplii.