Freshly fertilized ova, eyed ova and yolk-sac fry of brown trout, Salmo truifa L., were exposed to each of four trace metals (aluminium: 6000 nmol I -I ; copper: 80 nmol I-'; lead: 50 nmol I-'; zinc: 300 nmol I-I) while held in flowing artificial soft-water media maintained at pH 4.5 or 5.6 and [Ca] 20 or 200 pmol I-'. In continuous exposure from fertilization, survival of ova was severely affected at pH 4.5 and [Ca] 20 pmol I -I , regardless of the presence of Cu, Pb or Zn; A1 reduced embryonic mortality and improved hatching success. High ambient [Ca] at pH 4.5 increased egg survival. At ' swim-up ', surviving fry exposed to A1 or Pb had lower whole body Ca, Na and K content, irrespective ofpH or ambient [Ca]. Cu reduced whole body Ca and K content at pH 5.6 and [Ca] 200 pmol-I, and whole body Ca, Na and K content in the other media. Zn reduced whole body mineral content at pH 5.6 and [Ca] 20 pmol I-'. Whole body Mg content was reduced by all trace metals at pH 5.6 and [Ca] 20 pmol I-', and by Cu at pH 5.6 and [Ca] 200 p o l I-I. Al and Cu impaired skeletal calcification at pH 5.6 at both ambient [Ca]; Pb only at [Ca] 20 pmol I-'. Zn enhanced calcification at pH 4.5 and [Ca] 200 pmol I-'. In the absence of trace metals, low pH reduced body Ca, Na, Kcontent and skeletalcalcificationat [Ca] 200 pmol I-'. The uptake ofCa, Na and K, measured at regular intervals from hatching was impaired to the same extent by all treatments at pH 4.5, irrespective ofambient [Ca] or trace metal presence. At pH 5.6, irrespective of ambient [Ca], Al, Cu and Pb impaired Ca and K uptake. The rate of Na uptake was reduced by A1 and Cu. Al-treated yolk-sac fry, exposed to low ambient [Ca] from 200-300"days post-hatch, suffered high mortalities regardless of pH. Ca, Na and K uptake was impaired by all treatments at pH 4.5, and by A1 and Cu at pH 5.6 in a similar exposure period. The development of the early stages of brown trout in the presence of trace metals is discussed in relation to recruitment failure in areas of soft. acid water.