A method for detecting a specific sequence of nucleotides in a DNA or RNA molecule. The nucleic acid sample is adsorbed onto a nitrocellulose filter and an appropriate DNA probe, which matches the specific sequence being investigated, is added. After a period of incubation any excess probe is washed off and the nucleotide sequence under investigation can be detected by autoradiography. This technique has been miniaturized and vastly scaled up in microarray technology.