The Roche Amplicor PCR kit was used to detect HIV-1 DNA in UK patients of known serostatus. Four false-negative and/or equivocal results were obtained from patients who were known to be anti HIV seropositive (Tosswill et al., 1994). Cells from the blood of these patients were shown to contain HIV DNA after extraction, concentration and amplification by nested PCR using primers flanking those in the kit. To determine whether DNA sequence divergence was the cause of these discrepancies, the gag region targeted by the primers in the kit was sequenced for specimens giving positive, equivocal and false-negative results. No greater degree of sequence divergence was found within the primer and probe target regions among the equivocals and false-negatives than among the positive control specimens. The few misleading results were probably attributable to low copy numbers of proviral DNA in these specimens. Sequences obtained from the target and flanking regions of the kit were sufficient to allow the genotype of the virus to be determined.