We describe a set of expression vectors, pEX-PINK/0-3, for high-level production of (un)fused target proteins. The vectors incorporate a 'pink' reporter element, which signals in vivo the expression status of a target gene. A target sequence is cloned between the lambda PL promoter and the downstream mammalian cytochrome b5 gene. Thermo-induction drives transcription of a dicistronic mRNA from which the target protein and cytochrome b5 are independently and concurrently synthesized. Positive expression is indicated by visual transformation of bacteria from a grey/translucent to a bright pink color derived from tandemly expressed holocytochrome b5. The signal can be monitored in vivo spectrophotometrically.