The present invention relates to a new synthetic process in which an alkyne and an azide react to form a radioisotopic bioconjugate construct. The reaction is particularly useful for producing compounds for use in imaging and radiotherapy applications. The present invention also provides bioconjugate labels and further relates to the use of these compounds in diagnostic and therapeutic methods. In addition, the invention provides a related process for introducing a radioisotopic halogen atom into a terminal alkyne.