Iron is very insoluble in seawater, thus precipitates readily, and it is not entirely clear what forms are ``bioavailable''---i.e., available for transport into the phytoplankton cells. ``Dissolvable iron,'' which is operationally defined and easily measured on board ship, was measured regularly in the patch to monitor the fate of at least one fraction of the iron pool over the course of the experiment. The highest concentration in the patch the day after it was initiated was 3.6 nM---in good agreement with the target concentration. This value decreased steadily each day, and had dropped below the detection limit of the method (2 nM) by the 4th day, apparently reflecting a net loss of available iron from the system (Martin et al., 1994). The detailed results of this aspect of the story await the time-consuming analysis of samples for the other iron fractions.