ABSTRACT: Fertilization bioassays with the sea urchin Arbacia spatuligera were used to assess the water quality of 9 marine coastal sectors in the Biobío Region (Southern Chile) and to investigate the relationship between fertilization and environmentalvariables (in situ pH, turbidity, dissolved oxygen and salinity), heavy metals (copper, cadmium and mercury) and organic compounds (oil and grease, lindane, aldrin, dieldrin, DDE, DDT and phenols). The fertilization (mean +/- standard deviation) ofA. spatuligera eggs in sectors with high organic discharges from fishmeal industries such as Rocuant (14.1 +/- 6.0%) and San Vicente (22.5 +/- 10.0%) was significantly lower (p &LT 0.05) than in the other sectors (Chivilingo, Coronel, Lenga,Talcahuano, Penco, Tomé, Dichato) (70.5 +/- 13.0%). Percent saturation of oxygen (r = 0.839), pH (r = 0.830), turbidity (r = -0.683) and oil and grease (r = -0.888) showed significant correlations (p &LT 0.001) with fertilization. Principal ComponentAnalysis (PCA) using standardized variables grouped fertilization with dissolved oxygen and pH (total variance of 2 first components explained 73.0%) and Linear Multiple Regression Analysis produced the following model: Fertilization = 30.001 +0.785(Percent saturation of oxygen) - 0.059(Oil and grease) (r² = 0.837; p &LT 0.001). Rocuant and San Vicente stations were grouped and separated from the rest by inverse PCA and then discriminated by Discriminant Analysis (Hotelling-LawleyTrace, p &LT 0.001). It was concluded in laboratory bioassays that waters of coastal sectors from Rocuant and San Vicente, with the highest levels of oil and grease and lowest oxygen concentrations, had a significant effect on the fertilization of A.spatuligera eggs.