Condoms from five manufacturers were subjected to controlled exposures of heat, humidity, and air and to different natural environments in five countries. Under aerobic conditions (condoms in permeable packages or unpackaged), stress properties declined. The relationship between rate of decline as a function of temperature was quadratic. Under oxygen-restricted conditions (foil-wrapped packages) at average storage temperatures of 30 degrees C and lower, strain properties declined with little or no significant change in stress properties. The effect is to cause condoms to become stiffer; high-breakage rates in use have been correlated with product stiffening. A new rationale for accelerated-aging tests to predict condom shelf stability is suggested, including a test to control the trend of condoms to stiffen. Silicone lubricant, impermeable packaging, and inclusion of antioxidants in the condom formulation can prevent or minimize aerobic breakdown of latex condoms. Specifying low-modulus condoms can prevent excessive stiffening.