This paper is concerned with the theretical background and implications of isobaric supersaturation and bubble formation in the microcirculation following an abrupt shift from one inspired inert gas to another. The use of more than one inert gas, simultaneously or sequentially, has become common in diving and presents risks as well as potential benefits. A review of microcirculatory model useds, theoretical approaches to decompression, and order of magnitude calculations indicates that present empiricisms are inadequate for predicting such supersaturation phenomena. This is true whether based on the familiar assumption of perfusion-limited behavior or its diffusion-limited counterpart. The "chromatographic" model used here, which considers both perfusion and axial diffusion in tissue cylinders, shows that these combined effects can produce unexpectedly high local supersaturation. The implications include new possibilities for the experimental evaluation of gas transport models as well as practical risks of inert gas shifts in diving and certain diagnostic procedures.