Summary o 1. Measurements of weight, dark adaptation and haemoglobin were made on 778 factory workers (528 men, 250 women) in September, 1941. All measurements were repeated on 347 of these subjects in July, 1942, and weights only were recorded on 521 of the subjects in September, 1943. 2. A gain of weight in both men and women was found between 1941 and 1942 and a slightly lower gain between 1942 and 1943. The gain was observed in men and women over the age of 20 as well as that anticipated in adolescents below that age. 3. The average haemoglobin value in 1941 was 99·1% for the men and 91·2% for the women. A slight increase in these values was found between September, 1941, and July, 1942, but this was probably due to a seasonal variation. 4. The average dark adaptation of the younger factory workers was slightly poorer than that of nurses and students of the same age examined in Cambridge. The administration of pellets containing vitamins A, B 1, C and D produced a slight but significant improvement in dark adaptation.