Until 1979, the out-of-hours chemical pathology service was the conventional on-call service in which the medical laboratory scientific officers (MLSOs) carried out analyses at the direct request of clinical staff. In 1980, during an industrial dispute, junior ward doctors were trained to use three simple instruments which are maintained by the chemical pathology department. In January, 1981, when the dispute was settled, the doctors continued to use these instruments. Analyses they could not make were done by the MLSO on call, but only after the requests were monitored by a chemical pathologist or biochemist. The result was an 80% reduction in the number of calls. When the monitoring was withdrawn in 1983, there was some increase in the number of MLSO calls, but this was still 35% less than that with the conventional system despite a 4-fold increase in the total number of analyses done out of hours between 1979 and 1984. Surveys in 1984 and in early 1985 revealed that most doctors preferred using the instruments to asking an MLSO to make the analysis.