Inheritance of Tuberculosis IT has been difficult in the past to evaluate correctly the evidence for the inheritance of tuberculosis or of tendencies which might facilitate infection. Obviously twins provide material which might give valuable evidence on this matter. The analysis of twins has been developed by F. J. Kallmann and D. Reisner (J. Hered., 34, 293; 1943), with highly significant results. 616 twins, 930 sibs, 74 half-sibs and 668 parents in 308 complete families containing twins have been statistically analysed regarding the incidence of tuberculosis. The chance of contracting the disease increases in strict proportion to the degree of consanguinity to a tuberculous patient. The fact that monozygous twins exhibit 16 times as much similarity in resistance as compared with dizygous twins when all criteria are considered indicates that heredity, probably of a multifactorial nature, influences resistance. The authors point out that resistance to the invasion of the bacillus may be different from the factors of resistance to the spread of the established disease. This is supported by the fact that while there is a difference of 1:16 between resistance to progressive disease, there is only a difference of 1:3·5 in resistance to any form of clinical tuberculosis in monozygous and dizygous twins. The authors are proceeding further with this important analysis.