Hi there, When `xtick = TRUE`, the x-axis in interaction plot is weird: with(ToothGrowth, {interaction.plot(dose, supp, len, xtick = TRUE)}) you may notice that the x-axis is position at line 1, and the labels at line 2. And when set par(mgp = c(-4, -2, -1)) The x-axis is also positioned at line 1, but the labels at line -1. When `xtick = FALSE`, according the source code of interaction.plot(), the mgp[2] set to 0, however, the labels is also at line 1 instead of line 0. I don't know whether those behaviors were designed. Best, Jinsong PS: > sessionInfo() R version 4.1.2 (2021-11-01) Platform: x86_64-w64-mingw32/x64 (64-bit) Running under: Windows 10 x64 (build 19044) Matrix products: default locale: [1] LC_COLLATE=Chinese (Simplified)_China.936 [2] LC_CTYPE=Chinese (Simplified)_China.936 [3] LC_MONETARY=Chinese (Simplified)_China.936 [4] LC_NUMERIC=C [5] LC_TIME=Chinese (Simplified)_China.936 attached base packages: [1] stats graphics grDevices utils datasets methods base loaded via a namespace (and not attached): [1] compiler_4.1.2 tools_4.1.2