In submerged carbon-limited autolysing cultures of Penicillium chrysogenum, round-ended yeast-like fragments became the dominant surviving morphological forms and a new equilibrium between cell lysis and growth was observed, termed as a phase of ‘cryptic growth’. The formation of yeast-like fragments and their cryptic growth represented the only way that enabled the fungus to cope with harsh environmental conditions and survive. The surviving morphological forms reverted to vegetative growth after carbon supplementation. The glutathione metabolism and formation of reactive oxygen species (ROS) were influenced by numerous endogenous and exogenous factors depending on the phase of growth. Consequently, no firm correlation between the redox status, ROS levels and the observed morphological and physiological characteristics of the cells was found. The Dioxygen Avoidance Theory of Cell Differentiation failed to explain the complex physiological changes observed prior to and during autolysis, and any possible intrinsic analogy between the autolysis of P. chrysogenum and the oxidative stress dependent apoptosis of higher eucaryotes was also questioned. Nevertheless, ageing yeast-like fragments accumulated ROS as a function of incubation time and seem to be promising objects for future apoptosis research in filamentous fungi.