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Multi-locus DNA fingerprints using an M13 probe were obtained for eight individuals of giant kelp Macrocystis pyrifera (L.) C. Ag. Collected from Monterey Bay, California. For each individual, DNA was extracted from a diploid blade and from ca. 10[SUP9] haploid spores that were released from four to five sporophylls. Viable or swimming released from one individual were pooled and referred to as a spore group. A total of 34 bands (4-19 kb) was detected in DNA fingerprints from the eight blades and eight spore groups, with individual blads or spore groups exhibiting 7-18 bands (mean = 12.6). One band (4.5 kb) was present in all 16 samples. Similarity indices were detected in 11-14 of the 16 samples. Similarity indices were calculated for all pairwise comparisons of fingerprints bands among all possible combinations of blades and spore groups. Mean similarity indices for the eight comparisons of the blades and spore groups. Mean similarity indices for the eight blades (0.51, SE = 0.032) and spore groups (0.56, SE = 0.031) were significantly lower than for the eight comparisons of the blade and spore groups from a single individual (0.86, SE = 0.052). The data indicate that DNA fingerprints can be used to measure genetic variation within populations of M. pyrifera because variation of DNA fingerprints associated with meiotic products (spores) of a given individual is small relative to variation observed among individuals within the population. Additionally, fingerprint variation between diploid vegetative tissue and haploid meiotic products may be a measure of genetic change due to recombination or DNA turnover mechanisms. [ABSTRACT FROM AUTHOR]