The sequence complexity of total poly(A) RNA from a higher plant system, soybean cultured cells, was determined. Labeled cDNA synthesized from the poly (A) RNA hybridized exclusively with the unique sequence component of total soybean DNA. Analysis of the hybridization reaction between cDNA and the poly(A) RNA template revealed three abundance classes in the poly(A) RNA. These classes represent 18, 44 and 38% of the poly(A) RNA and contain information for approximately 60, 1900 and 30 000 different 1400-nucleotide RNA molecules. From these results, the total sequence complexity of poly(A) RNA was estimated to be 4.5 × 107 nucleotides. Saturation hybridization of labeled unique DNA with RNA showed that the total cell RNA represents 12.4% of the unique DNA sequence complexity, or 6.4 × 107 nucleotides, while poly(A) RNA represents 8.7% of the unique DNA sequence complexity, or 3.3 × 107 nucleotides. Thus, it is estimated that 50-70% of total RNA sequence complexity is contained in poly(A) RNA in these cells.