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These experlments were carrled out because the close chemlcal sImllarlty of BOL and LSD suggested that BOL mlght block the LSD reactlon by competlng with LSD for receptor sltes.

Subjects used were 15 nontolerant former morphlne addicts, all Negro males who were In good physlcal condition who presented no evidence of major psychoses. Most of these patlents had had considerable experTence wIth LSD. They recelved, in randomized order, the following drug combinatlons: BOL placebo plus LSD placebo; BOL plus LSD; and BOL placebo plus LSD. The combination of BOL plus LSD placebo was not studled because of the shortage of BOL, and also because the results should be Identicsl with those descrlbed In the report dealing with the acute effects of BOL.

The dosage of 8OL was 2-4 mg./70 kg. of bodywelght and was glven wlth the LSD. Nine patients received. the higher dose. The dose of.LSD was O.5-1.5 mcga./kg-Smaller doses were used'in the first patients fested, because of the posslbility that the drugs might synerglzz.

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ATTEMPTS TO BLOCK LSD REACTION WITH BOL GIVEN SIMULTANEOUSLY WITHLSD

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Methods. Measurements Inciuded threshoid for kneejerks, pupillery dlameter, systolic biood pressure, the Abramson-Jarvik questlonnaire, and grading of mental effects using the scale prevlously described. The results are shown ln the table, a copy of which was sent with my letter of 8 March l957. It is obvious that there was no sigaliflcant blocking of the LSD reaction and no accentiustinn -s

UT If Concluslon. Admialstration of BOL slmultaneously wlth LSD does not block or accentuate the LSD reaction. There Is no reason to belleve that glving BOL after LSD wouid'glve any different results, since Ginzel and Mayer-Gross have reported that intravenous administration of BOL does not reverse the LSD reactlon. These results suggest that fhe aftenuaflon of the LSD reacilon observed after two days pre-treatment with LSD is due to the development of cross tolarance.

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