Sirs: A recently published paper1 reviews a flow technique that was initially described in 1985, based on the introduction of the sample between two air or inert gas bubbles in the flow analysis manifold2. This procedure generates a reproducible sample monosegment having restricted convection mixing with the carrier solution resulting in low dispersion of the sample during its transport to the detector, even with long residence times. Figure 1 compares flow patterns generated by three well known flow analysis systems. From the chemical point of view the monosegmented technique permits performing determinations under non-steady state conditions, ensured by the high timing reproducibility found in the monosegmented system due the presence of but two gas bubbles. This monosegmented system contrasts with the previous multisegmented systems (see Fig. 1B) originally described by Skeggs3. However, the main advantage of the monosegmented system is that the signal is obtained after allowing most of the reaction to take place, under the conditions of restricted dispersion of the sample (i.e. near the equilibrium state). From the physical point of view the steady state flow is more closely approximated by a monosegmented system than by the flow injection system.