Inbreeding is known to increase developmental instability in outbreeding plants, and it has been argued that phenotypic plasticity in response to environmental variation might be similarly affected. To investigate whether phenotypic plasticity is altered by inbreeding, an outcrossed group and three successive generations of inbred cultivated Phlox drummondii were grown in six different treatments (Control, Low Water, Low Nutrient, Early and Late Leaf Removal, and Small Pots). Twelve plant characters were measured to determine the effects of the treatments and inbreeding. For those characters where inbreeding level by treatment interaction was indicated, the amounts and patterns of plasticity were examined to determine the source of the interaction. Despite substantial evidence for inbreeding depression of plant vigor and fecundity, there was no indication of an increase in the amount of phenotypic plasticity with progressive inbreeding. There was also no evidence that inbreeding systematically disrupts the pattern of plastic response to the environment.