The potato glycoalkaloids chaconine and solanine are saponins consisting of a nitrogen-containing steroidal aglycone and an attached trisaccharide, which differs between the two compounds. Potato glycoalkaloids bind strongly to sterols and also function as cholinesterase inhibitors. Both chaconine and solanine are expressed in potato plants to varying degrees depending on environment and breeding and play a significant role in plant defense against fungi and pests. The interaction of these two compounds with mixed monolayers of dimyristoylphosphatidylcholine and cholesterol, ergosterol, and stigmasterol at the water-air interface is under study using surface pressure measurements combined with observation by Brewster angle microscopy. The interaction with the monolayer of chaconine, solanine, and equimolar mixtures of the two injected into the subphase has been studied. The interaction results in surface pressure increases that are significant and sensitive to the sterol structure. In addition, the effects of the equimolar mixture with monolayers shows some evidence for a synergistic interaction between the two glycolalkaloids which can be related to similar effects reported for their interaction with liposomes.