Don Turnbull reviewed "In Search of the Unknown" in issue No. 13 of the magazine "White Dwarf" (June/July 1979), and gave the module a rating of 9 out of 10. He compared this module to "Against the Giants" and "Descent into the Depths of the Earth", complimenting "In Search of the Unknown"'s "excellent format, for instance, and the comprehensive way in which the scenario is introduced. TSR's high quality has not been in any way compromised". Turnbull criticized the module's use of Roman numerals as references, stating that ordinary numerals do the job much better.