A study was undertaken to investigate the relationship of psychological state to blood sugar level in man, with particular reference to hypoglycemia or low blood sugar.The principal subjects were eleven psychiatric patients with a primary diagnosis of neurosis. These subjects were administered oral glucose tolerance tests in the laboratory.Further information was gained from three subjects who were required to sit glucose tolerance tests for medical reasons, and from two subjects, one a diabetic, whose blood sugar was monitored at home with the Eyetone / Oextrostix system.Psychological state was assessed by means of a 'Self Report Mood Questionnaire' which was especially developed for the tudy.Personality variables were measured with the Eysenck Personality Questionnaire.The data were first analysed for relationships between blood sugar level and mood factors using a correlational approach, and presented as a series of single case studies.Later the data were analysed for more general relationships between psychological response to the glucose tolerance test and intra-subject variables.Significant correlations emerged between at least one mood factor and blood sugar level for eleven of the sixteen subjects. The sign of the correlation varied from subject to subject.In the case of only one psychiatric subject was hypoglycemia thought to be of overall clinical significance. A number of significant correlations emerged between personality variables and other variables, but no clear cut relationships were found.The subject sample was both too small and too diverse for any definitive conclusions to be drawn as to the relative effect of blood sugar level on psychological state in either normal or abnormal populations.