The standard size of spinal needle is determined by the external diameter, but the important quality, the flow through it, is related to the internal diameter. Twelve needles for each 6 types of 25G spinal needles available in Thailand, namely Pencan (B. Braun), Pencil point (Portex), Whitacre (B-D), Spinocan (B. Braun), Quinke (B-D) and Terumo, were studied using randomized crossover design at 4 different pressure levels. Times required for appearance and drop of artificial CSF were compared among them. We found that the time required for appearance and to drop of CSF were significant different among different levels of pressure and also among different types of spinal needle. The times required for appearance and to drop of CSF may markedly vary especially at the low CSF pressure 9 (from 1.86 to 4.46 seconds and from 50.86 to 162.14 seconds respectively). This means that we should wait for a proper time for different types of spinal needle to judge that the spinal needle is not in a proper position.