In order to elucidate the relationship between SMON (subacute myelo-optico-neuropathy) and chinoform, we carried out comparative studies on the doses and total amounts of chinoform preparations on the both patients of SMON and non-SMON admitted in Hospital I where SMON is most endemic in Okayama Prefecture, during the period of 1968, 1969 and 1970, to the total of 7,374 cases, and those treated in 1969 at Hospitals P and Q located in other districts, amounting to 11,953 and 7,290 cases respectively, all inclusive of SMON and non-SMON patients. The results are briefly summarized as follows. 1. Of the SMON patients in Hospital I, the ratio of those not receiving chinoform administration prior to the onset of SMON to the total SMON cases proved to be 8 to 55 cases in 1968, 32 to 52 cases in 1969, and 2 to 7 cases in 1970, indicating that the incidence in 1969 is very high. What is more, there is a considerable difference according to the fiscal year, thus giving no uniform results. Even at Hospital P the administration of chinoform cannot be confirmed in 2 cases out of 15 SMON patients and at Hospital Q in 2 out of 5 cases prior to the beginning of neurological symptomes of SMON. 2. In the region around Hospital I there was observed the highest incidence of SMON in the first half of the fiscal year 1969, and thereafter the incidence decreased rapidly from the latter half of 1969. However, We can find no evidence as to substantiate changes in the chinoform administration from the results of chinoform administered to general non-SMON patients. 3. The ratio of SMON patients to the total cases treated with chinoform at Hospital I proved to be 13.9% in 1968, 29.6% in 1969, and 5.7% in 1970, and at Hospital P it was 2.7% in 1969 and at Hospital Q 1.8%. 4. As to the age range of general patients receiving chinoform, the incidence of those non-SMON cases proves to be highest in twenties and thirties irrespective of sex and this finding doesnot coincide at all with the known propensity of SMON being more apt to occur in females of middle age. 5. As is obvious from these findings, our comparative studies conducted on the effects of chinoform to patients in the three hospitals do not yield any evidence to prove direct relationship between the chinoform administration and the onset of SMON.