AbstractFragile X mental retardation results from the absence of a selective RNA‐binding protein, FMRP. Previous studies demonstrated that FMRP forms messenger ribonucleoprotein (mRNP) complexes to associate with translating polyribosomes, suggesting that FMRP is involved in regulating protein synthesis. We are now facing the changing questions: How does FMRP influence protein synthesis in the brain? What is the target for FMRP in learning and memory? How does the absence of FMRP cause misregulation of protein synthesis, which in turn leads to mental impairment in fragile X syndrome? Models for abnormal neuronal function as a result of misregulated translation due to the absence of FMRP are discussed. Microsc. Res. Tech. 57:145–147, 2002. © 2002 Wiley‐Liss, Inc.