Different influences, like changes in salinity and temperature, the effects of heavy metals like copper and mercury, and the influences of nitrate and silicate deficiencies on the shape, generation time, and yield of the marine plankton diatomBiddulphia sinensis were tested in batch cultures. Those cells which show multiple or missing setae are classified as seta-aberrant, teratological forms. Sudden changes in salinity and temperature (30–15%. S; 12–20°C) lead to no more than 5% of aberrant cells (control cultures below 1%). Heavy metals (copper and mercury) cause a significant increase of the generation time, a distinct decrease of the cell yield, and (in the case of copper) up to 50% of seta-aberrant cells. The cells die at concentrations of copper above 10−5M.l−1, though EDTA was added as chelant. At concentrations below 10−5M.l−1 of copper, addition of EDTA as well as an increase of temperature from 12 to 20°C cause a reduction of toxicity. During batch growth the cells adapt to mercury but not to copper. At mercury concentrations above 10−8M.l−1 the cells die, even if EDTA is added. Unlike in copper-treated medium, EDTA does not reduce the toxicity of mercury. However, a detoxicating effect (20 instead of 12°C) can be observed due to higher temperature. Silicate deficiency, like the influence of copper and mercury leads to an elongation of the pervalvar axes. Particularly at a temperature of 20°C bended pervalvar axes and sometimes lateral evaginations of the frustule will be formed; this does not happen under the influence of copper and mercury. Multiple setae never appear under silicate deficiency. Under nitrate deficiency more than 10% of the cells are seta-aberrant. The suitability ofBiddulphia sinensis for test experiments in shipboard cultures is shown. Water samples were tested on the lack of nitrate, silicate, and phosphate. The percentage of seta-aberrant cells, the generation times, and the yields were determined. Simultaneous lack of phosphate and nitrate causes up to 30% of teratological cells. The seta-aberrant cells always appear during the exponential growth phase.