Some methacrylates are known to be strong contact sensitizers. To determine the effect of side-chain length on sensitizing potential, we examined 11 derivatives with linear side chains from C1 to C18 in an experimental sensitization test in guinea pigs. The results showed an increase in the sensitizing potential with increasing length of the alkyl side chain from C1 to C12. The C12 derivative, lauryl methacrylate, showed the strongest sensitizing potential. Further elongation of the alkyl side chain of methacrylates resulted in a decrease in the potential. With respect to the side-chain-length-dependent sensitizing potential, the present results correspond well with the findings obtained with other compounds like primin, catechols, phenols, hydroquinones, and gallates.