For optimum process management, substrates and products should be monitored continuously, because substrates are expensive, and because catabolic repression can be avoided. The main problem is continuous sampling. A cross-flow, hollow-fiber filtration module is described for the removal of solid-free samples from the high-solids medium required for cephalosporin-C production. The solids-free medium then permeates through a membrane, and is transported through air-segmented flow systems which quantify glucose (enzyme electrode), ammonia (ammonia-selective electrode), phosphate (molybdenum blue spectrophotometry), sulfate (methylthymol blue/barium), methionine (sodium nitroprusside) and cephalosporin (direct u.v. absorbance). The methods for glucose, methionine and cephalosporin are described in detail. The system is controlled by computer.