An attempt has been made to develop an automated instrument that measures the turbidity change in gelation reaction of a solution containing endotoxin and Limulus amoebocyte lysate, and quantifies endotoxin by determining gelation time of the sample. This instrument monitors the ratio R (t) of the sequential to the initial transmittance of up to 64 samples simultaneously and independently at 10 s increments. As the samples are stationarily incubated at controlled temperature of 37±0.5°C, the objective judgement of gelation is provided without any disturbance from sample vibration. Defining gelation time as the time required to obtain 5% decrease of R (t), the well correlated calibration curve was obtained for endotoxin concentration from 1 pg/ml to 100 ng/ml. The coefficients of variation of the calculated endotoxin concentration were 5.64 to 14.1%. The judgement of gelation by this method agreed well with that by the conventional gel-clot method when the proper measuring time (about a half of that by the conventional method) was selected.
