In 1214 adult persons, the relationship between alcohol consumption, the "liver enzymes" and other metabolic parameters, including the serum lipids, were investigated. In 798 of the persons, glucose tolerance tests with measurement of plasma insulin were performed (young and old male and female adults, either volunteers or patients without liver-related diseases). There was a high correlation of the three transferases GOT, GPT and GGT not only with the reported alcohol consumption but also with the plasma insulin. Most of the insulin increase, however, occurred in that range of the three transferases which, so far, has erroneously been considered to be the normal one. The C-peptide showed the same behaviour. Plasma insulin was also raised in relation to overweight, but only in persons with the sum of the three transferases over 30 U/l, not in persons who did not drink alcohol and who had really normal transferases (sum of the three transferases below 30 U/l measured at 25 degrees C). The quotient of plasma insulin divided by the relative body weight (Broca Index) was constantly low in the range of really normal transferases (up to 30 U/l), thereafter rising significantly, but only in the range of the transferases so far erroneously considered to be the normal one (GOT to 17, GPT to 22, GGT to 28 U/l, thus sum up to 67). Serum glucose in the tolerance test also rose with the transferases but much less than the plasma insulin. The correlation between both GGT and the sum of the three transferases with the plasma insulin was significantly positive and independent of the relative body weight. It is concluded that overweight (which is generally believed to be the main risk factor for non-insulin-dependent diabetes), and insulin resistance (which leads to hyperinsulinaemia), are largely caused by the toxic effects of "normal" daily alcohol, more in the human male than in the female. Hyperinsulinaemia (which blocks lipolysis) is caused by a toxic effect of ethanol and its metabolites, independent of caloric input and overweight. Hyperinsulinaemia is at least in the human male at present, probably the most important cause of obesity. In obesity, caused by "normal" alcohol consumption, a vicious circle occurs: the enhancement of the triglycerides and, consequently, the free fatty acids leads to a further decrease of glucose utilization by the muscle. A continuously high glucose level has toxic effects: eventually the beta cells of the pancreas are exhausted.(ABSTRACT TRUNCATED AT 400 WORDS)