The corrosion inhibition of substituted pyridine derivatives and quaternized pyridines in the presence and absence of acetylenic alcohol synergists is reported. Electrochemical Frequency Modulation (EFM) was used as a method of monitoring corrosion rates of steel in acidic environments. Causality factors were analyzed in order to determine if the occurrence of pitting could be evaluated in real time without invasive inspection of the metal sample. Pitting was also evaluated via scanning electron microscopy (SEM) for comparison of the variance in causality factors to observed pit formation. EFM was found to be a reliable and accurate method of monitoring general corrosion rates over time and a slight correlation was found between causality factors and pitting observed via SEM. In addition the pyridine derivatives were found to have complex substituent effects on corrosion inhibition with unsaturated substituents most significantly enhancing the performance relative to pyridine. Nearly all of the benzyl quaternized pyridine derivatives performed similarly to non-quaternized derivatives in the acid media suggesting similar mechanisms of action except for the N-benzyl quinolinium quaternary amine which displayed significantly enhanced behavior relative to the amine. The alkynol synergists gave similar efficacies under the test conditions regardless of chain length or conformation. Substitutent effects on the pyridine ring showed varying interactions with alkynols in pyridine-alkynol blends with both synergistic and antagonistic effects being observed.