Following a 7‐day control period, five male volunteers consumed a weight of propylene glycol alginate corresponding to 175 mg/kg body weight for 7 days, followed by 200 mg propylene glycol 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 propylene glycol alginate had little effect on faecal parameters (pH, water content, daily wet and dry weights). The dietary transit time remained constant for three volunteers, increased for one, and decreased for one. The ingestion of propylene glycol 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 propylene glycol alginate at a high level for 23 days caused no adverse dietary or physiological effects; in particular, the enzymatic and other sensitive indicators of adverse toxicological effects remained unchanged.