Recognition of specific protein antigens leads to immunological memory of antigen, whereas recognition of danger signals by the innate immune system determines the size, nature and longevity of a response. Recent data indicate that recognition of danger might have long-lasting effects on CD8 memory T-cell populations, specifically enhancing early cytokine release and thus altering the nature of subsequent immune responses. Here, a modified model of immune regulation is proposed in which a nonspecific immunological memory of danger accumulates during maturation of the immune system, allowing more potent cell-mediated immunity to develop in dangerous environments. Such a mechanism could be involved in phenomena leading to the 'hygiene hypothesis'.