The capacity factors (k′) were determined by reversed phased high-performance liquid chromatography (RP-HPLC) on a C18column for 18 substituted indoles. The linear relationship between the (k′) values and the percentage of the methanol in the eluent was tested for each compound. The molecular connectivity indices and quantum chemical parameters were calculated for the tested chemicals and used to develop quantitative structure-retention relationships (QSRR).