The pattern-triggered immune (PTI) response in plants is caused by the recognition of conserved microbe‐ or pathogen‐associated molecular patterns (MAMPs) by plant pattern recognition receptors at the cell surface. The goal of this study was to develop a simple, robust assay to quantify the PTI response in maize and to determine whether it could be used to predict levels of disease resistance. Flg22, an epitope derived from bacterial flagellin, is a commonly studied MAMP. We developed a seedling growth retardation (SGR) assay by which we could measure growth retardation in maize seedlings exposed to the bacterial MAMP flg22. We observed variation across 21 maize inbred lines. We used 161 lines from a recombinant inbred line (RIL) population derived from a cross between the lines CML228 (a high responder) and B73 (a low responder) to map quantitative trait loci (QTL) for this response. We found heritable variation in the RIL population and identified flg22 response QTL on chromosomes 1, 2, and 8. We did not observe strong correlations between SGR traits and levels of flg22-induced reactive oxygen production or with other disease resistance or defense response traits we had previously measured in the same population. We discuss the implications of these findings. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .