The acute toxic action of a number of common chemicals was tested by their ability to cause detachment of cultured mouse neuroblastoma C1300 cells. A TD25 value was obtained by graphic estimation of the concentration needed to cause 25% of the total cell number to detach. These TD25 values were compared with LD50 values obtained from the literature, and they were found to correlate with a coefficient of 0.86. For six of the tested substances—diuron, butylated hydroxytoluene, benzidine, cyclophosphamide, Na2SeO3, and KCN‐a very poor correlation was obtained. These diverging results could be ascribed to deficiencies in the neuroblastoma cell detachment test and emphasize the necessity for combinedin vitrotest procedures.