In the January issue of Pediatrics (p. 118), Drs. Cooper and Martin described a child with probable scotochromogen (M. scrofulaceum) infection, whose signs and symptoms became evident after a primary smallpox vaccination. We studied the tuberculin skin test and the in vitro lymphocyte response in two children vaccinated during therapy for primary tuberculosis, with results which may be of interest to the authors and to other readers. All skin tests were done with freshly prepared PPD-S; the induration was recorded after 48 hours.