The adsorption of diazepam dissolved in distilled water, 5% dextrose solution, normal saline, Ringer's solution and lactate Ringer's solution on porous glasses with controlled surface area was investigated. The adsorption phenomena principally obeyed the Langmuir adsorption isotherm. The reciprocal plots of the amount of adsorption vs. concentration of diazepam suggested that the maximum amounts of diazepam adsorbed onto the glass surfaces were the same from four of the solutions, excluding the dextrose solution, but the adsorption strengths differed considerably. The decrease of the adsorption strength of diazepam in lactated Ringer's solution, Ringer's solution and normal saline compared with that in distilled water could be ascribed to the decrease of the activity coefficient of diazepam in these solvents.