An instrument is described which continuously monitors the deposition of microbial biomass on metal surfaces by measuring changes in heat transfer and fluid frictional resistance. The microcomputer-controlled system simulates conditions by maintaining the appropriate process fluid velocity (or pressure drop) and heat flux (or wall temperature) to any metal surface on which deposition is occurring. The combined thermohydrodynamic measurements provide a very sensitive, relevant measurement of deposition in terms of process equipment performance parameters. The computer system also permits periodic pulsing of heat for simulating those systems, such as pipelines, in which a continuous heat load is not applied. Other features include the following: 1) instantaneous measurements; 2) diskette storage of data; 3) surface accumulation is monitored as opposed to cell mass or numbers in the fluid phase; 4) measurements are nondestructive and nonintrusive (an optional test section is available for sampling the deposit); 5) tubing of any alloy may be used; 6) the microprocessor input/output permits flexibility in operation and control; and 7) offers the potential for determining deposit composition in situ. Summaries of industrial case histories using the instrument are presented.