In laboratory tests, Culicinomyces clavosporus gave similar control (ca 55%) of Aedes taeniorhynchus larvae in small containers partially filled with either dredged-spoil (1.8 ppt water salinity) or soil from an upland site (0 ppt water salinity) after 3 days when applied at 1x 105 conidia/ml. When applied at rate of 5 x 104 conidia/ml to 5 liters of distilled water in large containers filled with either soil type, C. clavosporus resulted in ca 45 and 86% control of Ae. taeniorhynchus larvae at days 1 and 5 posttreatment, respectively. Mortality of mosquito larvae in sentinel cages in the large containers of both soil types was 93% at 5 days posttreatment. In field tests, C. clavosporus conidia and hyphae applied at a rate of 1 x 1010 conidia/m2 to the surface of salt marsh pools (water salinities ranged from 10.0 to 13.2 ppt) produced 100% mortality of field-collected, 2nd instar Ae. taeniorhynchus larvae in sentinel cages in 3 of 5 treated pools within 24 hr after application, and 98% mortality of larvae in sentinel cages from the remaining pools within 72 hr posttreatment. Dissection and microscopic examination of larvae in laboratory and field tests confirmed infection by C. clavosporus, but in the field tests most larvae died before there was extensive mycelial growth of C. clavosporus in the hemocoel. Lagenidium giganteum did not infect Ae. taeniorhynchus larvae in laboratory tests conducted in different-sized containers filled with dredged-spoil (water salinity ranged from 1.6 to 1.9 ppt) and a field test in enclosures in a salt marsh pool (10.0 ppt water salinity).