While investigating the serum choline esterase activity in anxiety states, a series of successive new admissions to the Neurological Section of the Mill Hill Emergency Hospital were tested with a view to obtaining further information as to the types of cases giving abnormally high or low esterase activities.

Sera giving abnormally high esterase activity were generally found to come from patients who had been diagnosed on admission as anxiety states, but an exception was noted particularly in the case of one patient (P. M—) with the very high esterase activity of 169. This patient was described on admission as “always emotional; he feels like weeping when the National Anthem is sung; not afraid of dangers.” He complained of uncontrollable weeping in company and he had considered suicide. Both from our own observation and from that of others it appeared that he was not a particularly anxious person, but he was extremely depressed. This observation raised the question of whether anxiety is the only emotional condition in which the serum esterase activity is raised or whether it may not also be raised in severe depression.

It appeared that information on this point might be obtained by analysing the data which had accumulated in testing the new admissions, which consisted of a varied collection of patients suffering from anxiety states, depressive states, hysteria and other neurological and mixed conditions. The possibility of subsequent analytical treatment was not considered at the time when the data were collected and the diagnoses were made by more than 12 different physicians who were known to differ to some extent in their diagnostic criteria. For this reason it was hardly expected that the results would be extremely clear-cut, but in actual fact the analysis brought out surprisingly clearly the differences in serum choline esterase activity in different types of neurotics. The diagnoses were made without a previous knowledge of the esterase activities and were therefore unbiased in this respect; we are indebted to the physicians for their permission to make use of them.

Methods.—The method of estimating the serum choline esterase was the same as was described in the preceding paper (Richter and Lee, 1942), except that venous blood from the arm was used instead of capillary blood. In some of the estimations acetylcholine bromide was used instead of the chloride. The bromide ion caused a slight inhibition of the enzyme which was corrected by multiplying by the factor 1·06, which was determined empirically by carrying out estimations on the same sample of serum with the chloride and bromide at the same time. The control group consisted of the 12 normal and 12 surgical patients described in the preceding paper; the mean serum esterase activity for the 24 controls was 75 units. The various esterases occurring in blood have been described by Richter and Croft (1942).