In six young hospitalized men the effect of a high dietary sugar intake (mean sugar content was 52.5 kcal% on a 2850 kcal-diet) on body-weight, body fat ratio (calculated from body density) and some metabolic and regulatory indicators was investigated. Although there was a great individual variability of values, a statistically significant increase of the body fat was recorded on the zznd day on the high-sugar diet (from k1.0 to 2.1%); a statistically significant increase of cholesterol, triglyceride and esterified fatty acid levels was recorded on the loth day, phospholipids did not change. Two weeks after discontinuation of this diet the investigated indicators practically returned to normal levels. After 24 days on the diet a slight increase of the insulinaemia on fasting was recorded and in four subjects higher maximum values of insulinaemia were obtained after half the amount of glucose. An increased catecholamine excretion was found : of noradrenaline (significant on the 3rd and 10th day on the diet) and of vanilylmandelic acid (significant on the 3rd and 17th day on the diet).Epidemiological investigations revealed a high ratio of sugar in the contemporary diet of man [e.g. I, 21 and demonstrated for instance in the Czech population a rising trend of sugar consumption.Conclusions on the negative effect of a high sugar consumption can be drawn e.g. from the positive association between sugar consumption and the prevalence of ischaemic heart disease (IHD) which was repeatedly demonstrated by YUDKIN [4-6 and others] and which was recorded also under our conditions [3].Many workers studied therefore in more detail the relations between sugar intake and blood lipid levels which are commonly considered indicators of the risk of atherasclerosis: Between the sugar intake and blood lipid levels positive associations were found which suggest relationships between triglyceride and cholesterol levels and sugar consumption [7-111. Other workers studied the mechanisms of this effect. Thus attention was drawn e.g. to the possible participation of insular stimulation in this sucrose-induced hyperlipogenesis [IZ] . For the interpretation of the mechanism of the effect exerted by sugar on the development of IHD the increased adhesiveness 24