Following intranasal administration to rats, wheat germ agglutinin-horseradish peroxidase (WGA-HRP) concentrated in the olfactory nerve and glomerular layers of the olfactory bulb resulting in a mean olfactory bulb concentration of 140 nM. A negligible amount of label was detected in the olfactory bulb following intravenous administration of WGA-HRP or intranasal administration of unconjugated HRP. This is the first quantitative assessment of intraneuronal transport of a protein into the brain using the olfactory route.