There are reasons to believe that changes in the secretion rate of saliva as well as changes in its protein and electrolyte composition promote the growth of micro-organisms associated with oral disorders. Knowledge of the electrolytes in the saliva of those with hyposalivation might therefore be of value in designing oral health-promoting measures. In this study, electrolytes in stimulated whole saliva were analysed in individuals with hyposalivation due to radiation therapy in the head and neck region (RT group), primary Sjögren's syndrome (pSS group), neuroleptic treatment (Neuro group), and to medication or of unknown origin (Unknown group). The bicarbonate concentration was significantly lower in all four hyposalivation groups compared with controls. The bicarbonate concentration, which in normal conditions is positively correlated with the salivary secretion rate, was lower in the Neuro group than in the RT and Sjögren's groups despite a stimulated secretion rate about twice as high. Furthermore, the Neuro group had the highest phosphate concentration. The RT and Sjögren's groups tended to have increased sodium concentrations. For potassium and calcium, the RT group had significantly higher concentrations than the other hyposalivation groups and the controls. The substantial increase in calcium and decrease in bicarbonate suggest that the function of the parotid glands is more affected than that of the other salivary glands. The results also indicate a contribution of plasma to the electrolyte concentrations determined in whole saliva in the RT and Sjögren's groups. In conclusion, in individuals with hyposalivation the concentrations of electrolytes in stimulated whole saliva seem to be more related to the reason for the hyposalivation than to the salivary secretion rate.