Floating calcium alginate capsules containing Lagenidium giganteum and 1% ground cork gave higher levels of control of Anopheles quadrimaculatus larvae in a 100-cm column of water than sinking capsules containing no cork. There was no significant difference between the cork capsules and the sinking capsules in the infection of larvae by the encapsulated fungus after storage (15 degrees C) for 57 days, although infectivity declined during that time from an initial infection rate of 100% to 35% and 40% for the cork and sinking capsules, respectively. Floating capsules containing glass bubbles were less effective than the cork capsules in the 100-cm column of water and had a shorter storage life than either sinking capsules or cork capsules.