Through the technical advances in molecular biology during the past decade, important new insights into the fundamental chromosomal changes associated with brain tumors have been gained. The pace of such research is accelerating, and most of the published reports have appeared outside the neurosurgical literature. Furthermore, many neurosurgeons may not be sufficiently familiar with the terminology and techniques involved to remain abreast of the field. In this review, we discuss through specific examples of recent work on brain tumors the basic techniques of molecular biology, including the Southern and Northern blots, restriction enzyme digestion of DNA, molecular cloning of genes, and mapping of chromosomal deletions. Gene amplification and rearrangements are discussed through review of recent work on the N-myc gene in neuroblastoma and the epidermal growth factor receptor (EGFR) gene in glioblastoma. The molecular cloning of the gli gene from a glioblastoma illustrates the powerful analytic nature of these laboratory techniques and the investigative potential of a cloned gene. The concept of the "recessive oncogene" is discussed through a summary of recent work analyzing restriction fragment length polymorphisms (RFLPs) in families of patients with meningioma, acoustic neurinoma, and bilateral acoustic neurofibromatosis (BANF; NF-2). Throughout this article, emphasis is placed on ways in which molecular biology may soon affect clinical practice.