A single-needle single-site technique for bone marrow aspiration and core biopsy has been compared with a two-needle technique, using 30 randomly selected patients who required these two investigations. In addition, two single-needle techniques were compared, aspirating immediately after penetrating the cortex or, alternatively, aspirating after the needle (without the stilette) had been advanced 20-25 mm. The two-needle technique was found to be superior to either of the single-needle techniques, which often resulted in a biopsy specimen that was denuded of bone marrow cells.