Four acute tests (96-h) with juvenile fish and four early life stage tests with embryos and larvae were completed with rainbow trout (Salmo gairdneri). Ninety-six-hour flow-through LC50 values for juveniles ranged from 8.1 to 10.9 mg/l nickel. Two early life stage tests were started with newly fertilized eggs, one test was started with eyed eggs and one test was started with pre-swim-up larval fish. No observed effect levels (NOEL), the highest nickel concentration without statistically significant adverse effects, for the two tests with newly fertilized eggs were less than 35 and 35 ug/l. The NOEL for the tests starting with eyed eggs and larval fish was 134 ug/l nickel. Early life stages were most sensitive when newly fertilized eggs were initially exposed, followed in sensitivity by eyed eggs, larval fish and juvenile fish.