ABSRACT:The goal of this study was to evaluate whether short 1 h sublethal assays may predict the results of 24 h lethality assays with rotifers Brachionus calyciflorus and anostracan crustaceans Thamnocephalus platyurus. The test bionts were hatched from cysts. Inhibition of ingestion was observed after 15 min of incubation of rotifers and crustaceans with the suspension of carmine and latex beads, respectively. Nine compounds with different modes of action were used as toxicants zinc ions, sodium dodecyl sulphate, p-nitrophenol, 3, 5-dichlorophenol and pharmaceuticals propranolol, fluoxetine, abamectin, doramectin and ivermectin. The toxicity values observed in the ingestion tests were very close to the mortality values over a wide range of toxicity from a low toxic surfactant to very toxic avermectins. The ratio between the 1 h EC 50 's in the ingestion test and the 24 h LC 50 's in the lethality test was below 2 in all cases for rotifers, and 7 in 9 cases for crustaceans. The toxicity of zinc and 3,5-dichlorophenol in the Thamnotoxkit F™ was 15-fold higher and 10 fold lower than in the ingestion test, respectively. The 24 h LC 50 values are within the range of 25-400 % of the 1 h EC 50 values for almost all toxicants tested with the exception of p-nitrophenol for B. calyciflorus and zinc and 3, 5-dichlorophenol for T. platyurus. Short, 1 h ingestion assays Rotoxrapid and Rapidtoxkit are good predictors of the mortality over the next 24 h and can be used as a range finding tests for representatives of pharmaceuticals and surfactants.