This study was conducted to describe the acute lethality and latent toxicity of didecyldimethylammonium chloride (DDAC) on early life stages of white sturgeon (Acipenser transmontanus). Fish responses to 0, 10, 50, 100, 250, 500 microg/L concentrations of DDAC were determined using a 96-h standard static renewal method for acute toxicity testing, with three replicates per concentration. Twenty fish per replicate were tested for 3, 11, and 42-d-old larvae, and 7 fish per replicate were tested for 78-d-old juveniles. Following exposure, survival and growth were evaluated in exposed fish raised in clean water for 2 weeks. The 96-h median lethal concentration (LC50) values for DDAC were 10.0 to 50.0, 58.5, and 99.7 microg/L for 3, 11, and 42-d-old larvae and 100 to 250 microg/L for 78-d-old juveniles. Significant decreases in larval growth and survival were noted at all tested concentrations and in all sturgeon age groups. Results of this study reveal age- and concentration-dependent responses to DDAC. Among the age groups tested, the 3-d-old larvae were the most sensitive group. Results also revealed that 96-h lethality testing alone is not adequate for determining the toxicity of DDAC to white sturgeon.