Inconsistencies in population estimates of temporary pond Aedes spp. Led to test of the efficiency of the Enfield sampler. With the samplers in place for 24 hr, only 41% of stage I Ae. Vexans were collected after 1 hr. This was largely due to stage I larvae remaining below the trapping vessel. However, after 24 hr no more than 6% of the larvae are below the trapping vessel. The largest potential source of error is operational inefficiency when stage I larvae are present, and considerable care must be exercised when handling these samples.