We found that half-oxidized hemoglobins such as (alpha 2+ beta 3+)2 and (alpha 3+ beta 2+)2, and methemoglobin were significantly increased in the erythrocytes of workers handling chemical compounds in a chemical plant of Japan. In addition, we found two unusual anodic hemoglobins (hemoglobin X and hemoglobin Y) to be present to a large extent in the erythrocytes of the workers investigated (21 persons), using isoelectric focusing electrophoresis on polyacrylamide gel plates. For example, the hemoglobin analysis of a worker showed: hemoglobin X, 6.2%; hemoglobin Y, 26.8%; hemoglobin A + hemoglobin F, 54.5%, half-oxidized hemoglobins, 9.8%; methemoglobin, 1.5%; hemoglobin A2, 2%. Since contents of hemoglobin A decreased by more than 40% of normal levels, and those of oxidized and modified hemoglobins increased up to 40% of total hemoglobins in the erythrocytes of several workers in the plant, we may consider these cases as ones having toxic methemoglobinemia with oxidized and modified hemoglobins. The changes of intracellular hemoglobins in these cases may be due to oxidation and modification of the proteins by chemical compounds absorbed from skin and lungs. Therefore, these hemoglobins may be a good indicator to monitor the health of workers in chemical plants. We also studied the formation mechanism of modified hemoglobins such as hemoglobin X and hemoglobin Y, investigating the reactions of hemoglobin with various aromatic compounds in vitro. On the other hand, we had the opportunity to analyze the changes in oxidized hemoglobins and modified hemoglobins in the blood of a man who drank cresol solution to commit suicide and was sent to a hospital.(ABSTRACT TRUNCATED AT 250 WORDS)