Our research objective was to characterize the biochemical effect of streptomycin during postnatal rat cerebral cortex development using a sensitive method that preserves the in situ topological relationship. We found a decrease in the mannosylation of asparagine-linked oligosaccharides without affecting polypeptide synthesis, DNA synthesis or glucose and mannose disappearance from the medium in mini-tissue units derived from P5. In addition, the rate of Dolp-GlcNAc2 Man9 Glc3 synthesis and the oligosaccharide protein transferase activity did not change in the presence of the aminoglycoside. These findings strongly suggested that the alteration of protein mannosylation occurred downstream of G3 transfer to nascent polypeptides. Further, the mini-tissue units may be useful for the assessment of neurological toxicity of antibacterial agents.