1. 1. The taurine content of Mya arenaria maintained at full salinity varies considerably between individuals (3–13 mg/g dry wt.). There is an inverse relationship between size and taurine content of the tissue. 2. 2. Taurine is lost when Mya is transferred to water of low salinity. However, unlike Mytilus which sheds almost all of its taurine when placed in sea water of 5‰, Mya maintains much (> 50%) of its taurine at this salinity. 3. 3. Mya can take up labelled taurine from solution at full salinity but little at low salinities. Tissue analysis and autoradiography show that most of the labelled sulphur is present in the gill and palp with smaller amounts in digestive gland and mantle. Injection of taurine and methionine resulted in a similar distribution. 4. 4. Starved Mya having been kept at low salinities for 3 weeks and then returned stepwise to full salinity show no evidence of increase in taurine content.