The influence of molecular biology in the field of allergy and immunol
ogy is becoming more pronounced. Both clinical and basic science inves
tigations use molecular biologic techniques to diagnose deficiencies a
t the molecular level and to elucidate the nature of the immune respon
se. An understanding of the basic biologic processes that underlie thi
s new technology is essential to the appreciation of its impact and us
efulness. This article provides an overview of these processes along w
ith pertinent applications.