In 26 patients with severe factor infertility (total spermatozoa per ejaculate 0.8-6.3 million) in vitro fertilisation was performed using a capillary tube culture system. Spermatozoa were concentrated and incubated with oocytes in a very small volume (10-20 microliters) within capillary tubes. In seven out of 26 patients (27%) at least one oocyte could be successfully fertilised (overall fertilisation rate 11.6%, 22/190 oocytes) and in two patients a pregnancy with the birth of a healthy child could be observed. If sperm progression was only of grade 2 or less no fertilisation could be observed in 10 patients with a total of 75 oocytes. The described capillary technique for in vitro fertilisation using very small volumes for sperm-oocyte culture may be useful in cases of severe oligozoospermia or before considering extreme therapies such as donor insemination of sperm microinjection.