1. Nonfaecal and faecal losses of Lichia amia were determined under controlled laboratory conditions at 15, 20 and 25 degrees C. 2. Ammonia-N was the major form of nonfaceal nitrogen excreted by L. amia and excretion rates were temperature-dependent. 3. The mass component b of the mass/ammonia-N excretion equation was temperature-independent and ranged from 0.63-0.65 and from 0.66-0.73 for starved and fed fish, respectively. 4. Mean nonfaecal energy loss (exogenous plus endogenous) was 3.78 +/- 1.99% of the ingested energy. 5. Assimilation efficiencies varied between individual fish and ranged from 61.24-93.79% (mean 80.76 +/- 7.14%) for dry matter and 87.52-98.22% (mean 94.09 +/- 2.22%) for energy. 6. The mean nonfaecal and faecal energy loss was 23.11 +/- 1.67% of the ingested energy.