Fathead minnows (Pimephales promelas) were exposed to a range of pH and Al concentrations in soft water (8 mg Ca/L) to determine effect levels at various life stages. The tested pH levels ranged from 8.0 through 5.2 and inorganic monomeric Al from 15 through 60 micro g/L. Reproductive processes including spawning, embryogenesis and early larval survival were more sensitive to acid stress than were juvenile growth and survival. Juvenile survival was significantly reduced at pH 5.2 + 60 micro g Al/L (P <0.05). Spawning success was reduced at pH 6.0 and 5.5 (P <0.10) and failed completely at pH 5.2, regardless of Al concentration. The effect of parental exposure on progeny survival was assessed by an interchange of embryos from the spawning treatment to all tested exposure conditions. When reared at pH 8.0 + 15 micro g Al/L through 6.0 + 15 micro g Al/L or at pH 5.5 + 30 micro g Al/L, parental exposure did not significantly influence progeny survival. However, survival was significantly reduced among progeny from brood fish reared at pH 5.5 + 15 micro g Al/L as compared to those spawned at pH 6.0 + 15 micro g Al/L and above, or at pH 5.5 + 30 micro g Al/L (P <0.05). Juvenile or 15 day larval growth effects were not detected under any exposure condition (P <0.05). Ultimately, fathead minnow young-of-the-year recruitment and production potential can be expected to diminish when environmental pH falls to 6.0 and to fail completely at 5.5 and lower. (Copyright (c) 1989 Kluwer Academic Publishers.)