Neurobiology. In the article “Long-term potentiation involves increases in the probability of neurotransmitter release” by Paul E. Schulz, which appeared in number 11, May 27, 1997, of Proc. Natl. Acad. Sci. USA (94, 5888–5893), the author has pointed out that lines 14 and 15 of the abstract contain a printer’s error: Ip should be p.