Following a 7‐day control period, five male volunteers consumed a weight of sodium alginate corresponding to 175 mg/kg body weight for 7 days, followed by 200 mg sodium alginate per kg body weight for a further 16 days. Measurements before and at the end of the 23‐day period of dietary supplementation showed that sodium alginate acted as a faecal bulking agent for all volunteers, giving a significant(p< 0.01) increase in daily wet weight, and also increases in the water content and daily dry weight, but no change in faecal pH. Although the dietary transit time remained constant for two volunteers, it decreased for two, and increased slightly for one, with little resulting change in the overall mean value. The ingestion of sodium alginate had no significant effect on (a) haematological indices, (b) plasma biochemistry parameters, (c) urinalysis parameters, (d) blood glucose and plasma insulin concentrations, (e) breath hydrogen concentrations. No allergic responses were reported by, nor observed in, any of the volunteers. The study therefore indicates that the ingestion of sodium alginate at a high level for 23 days caused no effects other than those normally associated with a polysaccharide bulking agent; in particular, the enzymatic and other sensitive indicators of adverse toxicological effects remained unchanged.