The reaction of leaf growth to drought stress is controlled by various hormones, among which ABA is one of the most important. The aim of this study was to examine the effects of ABA deficiency on tomato leaf response under severe drought stress. Therefore, ABA-mutant (flacca) and wild type (Ailsa Craig) were selected for research and in the stage of second flower truss anthesis plants were exposed to severe water deficit. The effects of severe drought on wild-type leaves and flacca mutant showed that, as a result of reduced ABA concentrations, flacca plants were exposed to a higher degree of stress than wild-type leaves, which had a negative impact on the examined physiological and biochemical parameters. Severe drought caused stomatal closure, decreased water potential, specific leaf area, and chlorophyll concentrations in the leaves in both genotypes, but this was more pronounced in the mutant. Wild-type plants have accumulated more vitamin C and ABA and have a higher total antioxidant capacity in the leaves in dry conditions than flacca mutants, which contribute to their better adaptive response to stress. Based on this, it can be assumed that the ABA mutation has led to a decrease in the capacity for oxidative stress products caused by severe drought stress.