Because many different types of phantoms had been used to calibrate "in vivo" counting systems, the importance of establishing standard specifications for phantoms was emphasized at the 1990 international meeting of "in vivo" counting professionals held at the National Institute of Standards and Technology (NIST). The consensus of the meeting attendees was that standard specifications were needed for the BOMAB phantom. The standard specifications for the BOMAB phantom provide the basis for a consistent phantom design for calibrating "in vivo" measurement systems. Such systems are designed to measure radionuclides that emit high-energy photons and that are assumed to be homogeneously distributed in the body.